Weblogic,EJB, $Proxy99 class cast exception - ejb-3.0

Question

Following are the modules in my project,
1. EJB module (version 3): We prepare ejb jar of this module and deploy on Weblogic11g server. It deals with database operation. It has #local, #Remote interface and #stateless classes implementing #local,#Remote interfaces.
2. Web Application : This web application takes inputs (user uploads file) from users, validates file and inserts data into database. It uses RMI.
Problem: On production (weblogic 11g server ) sometimes we observe exception saying $Proxy99 cannot be cast to "Remote interface name" (for different different classes) e.g com.xyz.fileProcessSetting.FileProcessSttgFacadeRemote.
But after some time when we again upload file, it gets uploaded successfully without any error.
Now, I do not understand how come these remote objects becomes temporarily unavailable? Never faced this issue on development/UAT environment. Also no idea how to reproduce and fix it.
Please help. Thanks in advance.
#Remote
public interface FileProcessSttgFacadeRemote {
//methods
}
#Local
public interface FileProcessSttgFacadeLocal {
//methods
}
#Stateless
public class FileProcessSttgFacade implements FileProcessSttgFacadeLocal, FileProcessSttgFacadeRemote {
//methods
}
in weblogic-ejb-jar.xml
<weblogic-enterprise-bean>
<ejb-name>FileProcessSttgFacade</ejb-name>
<stateless-session-descriptor>
<business-interface-jndi-name-map>
<business-remote>com.xyz.fileProcessSetting.FileProcessSttgFacadeRemote</business-remote>
<jndi-name>FileProcessSttgFacade</jndi-name>
</business-interface-jndi-name-map>
</stateless-session-descriptor>
</weblogic-enterprise-bean>
In web application also in ejb module whenever we want to call methods we use following lookup method to get remote object:
public class someclass extends EjbLocator {
public void someMethod(){
FileProcessSttgFacadeRemote fpfr = (FileProcessSttgFacadeRemote) getService("FileProcessSttgFacade");
//other code
}
}
Following is the class used for JNDI lookup:
public class EjbLocator {
public Object getService(final String jndiName) throws Exception {
try {
obj = getDefaultContext().lookup(jndiName);
} catch (final Exception exp) {
exp.printStackTrace();
}
return obj;
}
protected Context getDefaultContext() {
try {
final Hashtable<String, String> env = new Hashtable<String, String>();
env.put(Context.INITIAL_CONTEXT_FACTORY, "weblogic.jndi.WLInitialContextFactory");
env.put(Context.SECURITY_PRINCIPAL,"weblogic");
env.put(Context.SECURITY_CREDENTIALS, "password");
env.put(Context.PROVIDER_URL, "t3://<ip>:<port>");
defaultContext = new InitialContext(env);
return defaultContext;
} catch (final NamingException nExp) {
nExp.printStackTrace();
}
return null;
}
}