I was also facing the same problem. I just want to share my experience with you all. It is right that the actual exception is not mentioned in this aforesaid exception. To reveal that exception I have used wlspy.jar tool. Using this tool I got the inner sql activity in configured log file. Due to which I got the hidded sql constraint exception.
Steps to Configure:
1) Add wlspy.jar in your weblogic server classpath.
2) Add configurations related to wlspy in database source.
For example:
jdbc:bea:DB2://db2host:50000;spyAttributes=(log=(file)/opt/bea/logs/mySpy.log;timestamp=yes)
After that restart your weblogic server and do the activity. You will get database related logs in mySoy.log file. In my case I got the actual constraint exception.
Go through this link:
http://docs.oracle.com/cd/E21764_01/web.1111/e13753/spy.htm#JDBCD469