I have a situation involving a mixed TCP-IP and IPX environment, running
SQL7.0SP0 on NT4. We are using integrated security. Domain logins are
associated with local groups on the server machines and those local
groups are granted access via EM. We have some 6.5 machines hanging
around, but they do not seem to exhibit the behavior.

We prefer to use multiprotocol, but certain machines give an error:
"Login Failed for user '(null)'. Reason: Not associated with a trusted
SQL Server Connection.

If multiprotocol is not working, then the TCP/IP network library won't
work either. If we switch over to named pipes, we can connect with no
further problems.

Here's the really strange part: sometimes we can connect just fine. For
example, last week I could not connect to one of our machines using
multiprotocol. Today, I can. Two days from now, I might lose my ability
to connect. Nothing obvious is changing on the server.

Questions:

Can this be some sort of a security/permissions problem with
the RPC running on the server?

Are there User Rights (Under Policies in the NT User Manager) that need
to be set up for a group? Security was cranked down pretty hard on these
machines, is it possible that someone removed some crucial Right from
the Everyone group?

Could some router/firewall be intermittantly blocking some important
port?

Has anyone seen this before? I've checked through the archives at
deja.com, swynk.com and sqlpass.com without finding anything.