Seems to me like you are hitting a bug in 8.0.5, which are fixed in 8.0.6 or a 8.0.5.2 patch set , plz find some more info by a click on the following :

http://metalink.oracle.com/metalink/...p_id=32297.996

I think you wont be getting support of 8.0.5 from ORACLE.

If this doent help, may be you may need to an event in initi.ora, to check with the trace file for this error.

Thanks,
Madhu