Hi,
The instance connected to was terminated abnormally, probably due to a SHUTDOWN ABORT. The current process was forced to disconnect from the instance.
Start the instance and after the instance is started reconnect
Also see the alert.log file for a possible cause of instance failure.

In case of any help please be free to ask to me at [email protected]

regards,
Rohit Nirkhe,Oracle DBA,OCp 8i
[email protected]