Urgent help needed on losing connection

Dear All,
I am encountering a strange problem. We have a banking software which is an multi-tiered application. The application usually remains inactive for a long duration and with a sudden splurge of activity for sometime & inactive again.Suddenly when the client tries to connect we get the below mentioned error. The default setting of sqlnet.ora exists i.e. sqlnet.expire_time=0.The main problem therefore is that the application loses connection with the database frequently.

Kindly let me know if there is any parameter that actually looks at inactive clients/session for a long duration and kills them. I have not set any profiles for the users & therefore is at default.

Any suggestions will be of great help

Thanks & Regards,
Krishnananda

Error while browsing for events
Exception: EDBEngineError
DB Engine Error:
General SQL error.
ORA-01041: internal error. hostdef extension doesn't exist Total Errors: 2
Error (0)
 Message: General SQL error.
 NativeError: 0
 Category: 51
 ErrorCode: 13059
 SubCode: 3
Error (1)
 Message: ORA-01041: internal error. hostdef extension doesn't exist

 NativeError: 1041
 Category: 51
 ErrorCode: 13059
 SubCode: 3 Received on Thu Jan 24 2002 - 05:55:12 CST