DB Link Problem

We have a forms 4.5 form that our users query a remote database with. They keep the form (and session) up for days.90% of the time the query works perfectly but sometimes they get an error ORA-02068 FOLLOWING SEVERE ERROR FROM RHY where RHY is the db_link. The extended error is ORA-03114 NOT CONNECTED TO ORACLE and the next few times it will be ORA-03113 END OF FILE COMMUNICATION CHANNEL. Then all of a sudden it will work again after a few times with error. After the query runs I close the db_link. We use oracle 7.1 and the db_link connects to a 7.1 db. Any ideas I am really struggling with this one.

		thanks for any help or ideas,
				derek