Resolution:
When migrating TRA to 5.6.0, it failed with exception

java.lang.NoClassDefFoundError: org/apache/regexp/RESyntaxException
at com.tibco.objectrepo.vfile.streamfile.FileDirectory.do(FileDirectory.java:443)
at com.tibco.objectrepo.vfile.streamfile.FileDirectory.a(FileDirectory.java:463)
at com.tibco.objectrepo.vfile.streamfile.FileDirectory.getChildCount(FileDirectory.java:50)
at com.tibco.objectrepo.tool.AE4Migrator.a(AE4Migrator.java:229)
at com.tibco.objectrepo.tool.AE4Migrator.migrate(AE4Migrator.java:163)
at com.tibco.objectrepo.tool.Converter.migrateToAE4(Converter.java:633)
at com.tibco.objectrepo.tool.Converter.main(Converter.java:480)

After searching, we found that "org/apache/regexp/RESyntaxException" is located at "/usr/tibco/products/tpcl/5.6/tomcat/server/lib/jakarta-regexp-1.2.jar".

So, the workaround is to add "usr/tibco/products/tpcl/5.6/tomcat/server/lib" to RepoConvert.tra "tibco.class.path.extended". It is like TRA 5.5.2 RepoConvert.tra. Then it will work.