OK I think I remember...


1) The sqlnet.ora should have: (i'm using windows NT)
SQLNET.AUTHENTICATION_SERVICES= (NTS)

2) On the client ....
There should be a registry key called:
OS_AUTH_PREFIX_DOMAIN=FALSE

Set it in HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOME0

But there may be more then one home so try to create it in all HOMEX's

Give it a try. Otherwise I'm not sure.
MetaLink is the best resource on this search for 3113 or post a message there.
HTH