How to find the cause of a Maven build error? - maven

Question

I try to make a local Maven build.
% mvn help:effective-settings
[INFO] Scanning for projects...
Downloading: http://example.com/nexus/content/groups/public/org/springframework/boot/spring-boot-starter-parent/2.1.2.RELEASE/spring-boot-starter-parent-2.1.2.RELEASE.pom
[ERROR] [ERROR] Some problems were encountered while processing the POMs:
[FATAL] Non-resolvable parent POM for example.components.discovery:example-app:01-SNAPSHOT: Could not transfer artifact org.springframework.boot:spring-boot-starter-parent:pom:2.1.2.RELEASE from/to nexus (http://example.com/nexus/content/groups/public): Access denied to: http://example.com/nexus/content/groups/public/org/springframework/boot/spring-boot-starter-parent/2.1.2.RELEASE/spring-boot-starter-parent-2.1.2.RELEASE.pom , ReasonPhrase:Forbidden. and 'parent.relativePath' points at no local POM # line 12, column 10
#
[ERROR] The build could not read 1 project -> [Help 1]
[ERROR]
[ERROR] The project example.components.discovery:example-app:01-SNAPSHOT (/Users/me/workspace/example-app/pom.xml) has 1 error
[ERROR] Non-resolvable parent POM for example.components.discovery:example-app:99.99.99-SNAPSHOT: Could not transfer artifact org.springframework.boot:spring-boot-starter-parent:pom:2.1.2.RELEASE from/to nexus (http://example.com/nexus/content/groups/public): Access denied to: http://example.com/nexus/content/groups/public/org/springframework/boot/spring-boot-starter-parent/2.1.2.RELEASE/spring-boot-starter-parent-2.1.2.RELEASE.pom , ReasonPhrase:Forbidden. and 'parent.relativePath' points at no local POM # line 12, column 10 -> [Help 2]
[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/ProjectBuildingException
[ERROR] [Help 2] http://cwiki.apache.org/confluence/display/MAVEN/UnresolvableModelException
Some noticeable facts:
I get the same error on other projects with the same Spring dependency.
Co-workers don’t have this problem when they run a Maven build of the project.
Before introducing Nexus, the Maven build was run successfully, and so did for other Spring projects.
If there were some syntax errors in the settings.xml, the above error would show first and follow by complaints of syntax errors in the settings.xml.
My settings.xml seems to have the same structure as my co-worker’s who can run the Maven build successfully, the user credentials are different, of course.
The above facts eliminate all possible causes stated in the help 1 document. Among 6 possible causes stated in the help 2 document, the only possible cause is #4 given the above facts. We have a tool to generate the settins.xml file and use Maven encryption to encrypt the password for the file. I don't know how to verify whether the encrypted password is correct or not. Any other possible causes?