We see these errors in the RetainWorker log:
com.gwava.gweasysoap.GWSoapAPIException: End of file hit , Code: c002
The job aborts the mailbox and continues to the next mailbox.
With a customer we found a bad message in the user's mailbox. GWCheck was unable to fix it. A job run of the last few days of the user's mailbox showed that messages could be dredged.
Running a SOAP trace allowed us to discover which message was causing the error. The message was broken in WebAcc. Retention services needed to be turned off and the message deleted.