Java EE (Java Enterprise Edition) General Discussion

Hi,
When I trying to move a message from one folder to another, basically involved copy, delete, expunge actions, sometimes I got following error:

EXCEPTION: A17 NO EXPUNGE failed: Failed to expunge (Database error);
nested exception is:
com.sun.mail.iap.CommandFailedException: A17 NO EXPUNGE failed: Failed to expunge (Database error)

Sometime getting:
:EXCEPTION: A15 NO COPY failed: Failed to copy (Database error);
nested exception is:
com.sun.mail.iap.CommandFailedException: A15 NO COPY failed: Failed to copy (Database error)

Have anybody met the same problem before? What might be a reason. In my code, there are mult-threads operating on the same INBOX.

Thanks alot.