While compiling SOA composite in JDeveloper, I saw this error many times:
It happens mainly because of the Java code in the composite BPEL. Even after increasing the logging level of scac compilation, it didn't really show enough information to fix the problem. Here are some initial steps you can do to troubleshoot the issue (may be I will modify the scac task so we can show more information like 10g jdev used to show).
-> Check all imported libraries for composite project used by Java embed. If libraries are not found, jdev just shows SCAC-50012.
-> Make sure the java embed compiles fine by creating a sample Java project. If method signature changes or so, Jdev doesn't show any error, it just shows SCAC-50012.