Fix "Unsupported major.minor version 52.0" running mvn sonar:sonar against sonarqube 5.5 with java 7 - maven

Question

Dear knowledgeable fellows,
I got this java project dropped on me that worked for a number of colleagues. Our DoD requires certain Sonarqube results however and I can't get it to run properly on my machine.
I have both JDK's 7 and 8 installed. The thing is, my company requires everything to be done in Java 7 (and on windows 2008 server!), so I had to stick with Sonarqube 5.5, apparently the last version using 7. Installation is fine, service is running localhost website shows properly. The service runs this:
c:\tools\sonarqube-5.5\bin\windows-x86-64\wrapper.exe -s c:\tools\sonarqube-5.5\conf\wrapper.conf
... and starts up just fine. For completeness' sake, here is my sonar.properties (uncommented lines only):
sonar.jdbc.maxActive=20
sonar.jdbc.maxIdle=5
sonar.jdbc.minIdle=2
sonar.jdbc.maxWait=5000
sonar.jdbc.minEvictableIdleTimeMillis=600000
sonar.jdbc.timeBetweenEvictionRunsMillis=30000
... and here is my wrapper.conf:
wrapper.java.command=C:\Program Files\Java\jdk7\bin\java
wrapper.java.additional.1=-Djava.awt.headless=true
wrapper.java.mainclass=org.tanukisoftware.wrapper.WrapperSimpleApp
wrapper.java.classpath.1=../../lib/jsw/*.jar
wrapper.java.classpath.2=../../lib/*.jar
wrapper.java.library.path.1=./lib
wrapper.app.parameter.1=org.sonar.application.App
wrapper.java.initmemory=3
wrapper.java.maxmemory=32
wrapper.console.format=PM
wrapper.console.loglevel=INFO
wrapper.logfile=../../logs/sonar.log
wrapper.logfile.format=M
wrapper.logfile.loglevel=INFO
wrapper.syslog.loglevel=NONE
wrapper.console.title=SonarQube
wrapper.single_invocation=true
wrapper.ntservice.name=SonarQube
wrapper.ntservice.displayname=SonarQube
wrapper.ntservice.description=SonarQube
wrapper.ntservice.dependency.1=
wrapper.ntservice.starttype=AUTO_START
wrapper.ntservice.interactive=false
wrapper.disable_restarts=TRUE
wrapper.ping.timeout=0
wrapper.shutdown.timeout=3000
When my colleagues ran with Sonarqube 5.5, everything worked, but when I run "mvn sonar:sonar" against the exact same codebase, I get the following, which tells me about "org/sonarsource/scanner/maven/SonarQubeMojo : Unsupported major.minor version 52.0" which would indicate some requirement for java 8:
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building --project name obscured-- 1.0.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[WARNING] The POM for org.jboss.logging:jboss-logging:jar:3.1.4.GA-redhat-1 is missing, no dependency information available
[INFO]
[INFO] --- sonar-maven-plugin:3.2:sonar (default-cli) # project name obscured ---
[WARNING] Error injecting: org.sonarsource.scanner.maven.SonarQubeMojo
java.lang.TypeNotPresentException: Type org.sonarsource.scanner.maven.SonarQubeMojo not present
at org.eclipse.sisu.space.URLClassSpace.loadClass(URLClassSpace.java:115)
at org.eclipse.sisu.space.NamedClass.load(NamedClass.java:46)
at org.eclipse.sisu.space.AbstractDeferredClass.get(AbstractDeferredClass.java:48)
at com.google.inject.internal.ProviderInternalFactory.provision(ProviderInternalFactory.java:86)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.provision(InternalFactoryToInitializableAdapter.java:55)
at com.google.inject.internal.ProviderInternalFactory$1.call(ProviderInternalFactory.java:70)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision(ProvisionListenerStackCallback.java:100)
at org.eclipse.sisu.plexus.PlexusLifecycleManager.onProvision(PlexusLifecycleManager.java:133)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision(ProvisionListenerStackCallback.java:109)
at com.google.inject.internal.ProvisionListenerStackCallback.provision(ProvisionListenerStackCallback.java:55)
at com.google.inject.internal.ProviderInternalFactory.circularGet(ProviderInternalFactory.java:68)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.get(InternalFactoryToInitializableAdapter.java:47)
at com.google.inject.internal.InjectorImpl$2$1.call(InjectorImpl.java:997)
at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1047)
at com.google.inject.internal.InjectorImpl$2.get(InjectorImpl.java:993)
at com.google.inject.Scopes$1$1.get(Scopes.java:59)
at org.eclipse.sisu.inject.LazyBeanEntry.getValue(LazyBeanEntry.java:82)
at org.eclipse.sisu.plexus.LazyPlexusBean.getValue(LazyPlexusBean.java:51)
at org.codehaus.plexus.DefaultPlexusContainer.lookup(DefaultPlexusContainer.java:260)
at org.codehaus.plexus.DefaultPlexusContainer.lookup(DefaultPlexusContainer.java:252)
at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getConfiguredMojo(DefaultMavenPluginManager.java:462)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:119)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:120)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:347)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:154)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:584)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:213)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:157)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: java.lang.UnsupportedClassVersionError: org/sonarsource/scanner/maven/SonarQubeMojo : Unsupported major.minor version 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClassFromSelf(ClassRealm.java:389)
at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:42)
at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:259)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:235)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:227)
at org.eclipse.sisu.space.URLClassSpace.loadClass(URLClassSpace.java:107)
... 41 more
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.555 s
[INFO] Finished at: 2016-11-03T09:39:32+01:00
[INFO] Final Memory: 21M/310M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.sonarsource.scanner.maven:sonar-maven-plugin:3.2:sonar (default-cli) on project project name obscured: Execution default-cli of goal org.sonarsource.scanner.maven:sonar-maven-plugin:3.2:sonar failed: Unable to load the mojo 'sonar' in the plugin 'org.sonarsource.scanner.maven:sonar-maven-plugin:3.2' due to an API incompatibility: org.codehaus.plexus.component.repository.exception.ComponentLookupException: org/sonarsource/scanner/maven/SonarQubeMojo : Unsupported major.minor version 52.0
[ERROR] -----------------------------------------------------
[ERROR] realm = plugin>org.codehaus.mojo:sonar-maven-plugin:3.2
[ERROR] strategy = org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy
[ERROR] urls[0] = file:/C:/Data/maven/org/sonarsource/scanner/maven/sonar-maven-plugin/3.2/sonar-maven-plugin-3.2.jar
[ERROR] urls[1] = file:/C:/Data/maven/org/apache/maven/shared/maven-dependency-tree/2.2/maven-dependency-tree-2.2.jar
[ERROR] urls[2] = file:/C:/Data/maven/org/codehaus/plexus/plexus-component-annotations/1.5.5/plexus-component-annotations-1.5.5.jar
[ERROR] urls[3] = file:/C:/Data/maven/org/eclipse/aether/aether-util/0.9.0.M2/aether-util-0.9.0.M2.jar
[ERROR] urls[4] = file:/C:/Data/maven/org/sonatype/plexus/plexus-sec-dispatcher/1.4/plexus-sec-dispatcher-1.4.jar
[ERROR] urls[5] = file:/C:/Data/maven/org/sonatype/plexus/plexus-cipher/1.4/plexus-cipher-1.4.jar
[ERROR] urls[6] = file:/C:/Data/maven/org/codehaus/plexus/plexus-utils/3.0.22/plexus-utils-3.0.22.jar
[ERROR] urls[7] = file:/C:/Data/maven/org/sonarsource/scanner/api/sonar-scanner-api/2.8/sonar-scanner-api-2.8.jar
[ERROR] urls[8] = file:/C:/Data/maven/commons-lang/commons-lang/2.6/commons-lang-2.6.jar
[ERROR] urls[9] = file:/C:/Data/maven/com/google/code/findbugs/jsr305/2.0.3/jsr305-2.0.3.jar
[ERROR] Number of foreign imports: 1
[ERROR] import: Entry[import from realm ClassRealm[maven.api, parent: null]]
[ERROR]
[ERROR] -----------------------------------------------------
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginContainerException
What am I missing here?