Login failed for user (null). Reason: Not associated with a trusted SQL Server c

Login failed for user '(null)'. Reason: Not associated with a trusted SQL Server connection

Newbie here, so thanks in advance for any help. SQL Server 2000 on Windows 2000, Mixed Mode authentication IS enabled.

System DSN set on 8 workstations, a mix of 2000 - 98 and XP Pro

App uses DSN connection, specifies sa user and password. DSN's all set up the same, Client config is TCP/IP, SQL Server also set to only accept TCP/IP.

Trying to authenticate using SQL Server Authentication. XP Pro machines generate the above error. 98 and 2000 machines connect flawlessly.

I am stumped. Have read the MS knowledgebase articles, read threads here. Nothing seems to apply. It's an Internet app, so using Windows Authentication is not desired. I just don't understand why XP pukes while the other MS platforms connect just fine.

If anyone has any thoughts, I'd appreciate suggestions!

Thanks?? Double check those DSN connections. Also, don't use sa. That's really bad. Set up another username and password to use. Do you have anything not using the DSN's? What kind of an application is this? (VB,Access?)|||Thanks for reply. I know sa is bad - have a client with this issue, so I recreated it in my own intranet - so I used sa for testing. Yes, after setting up System DSN on all machines, I ran the "Test Connection" and the test passed on the all OSes, even the XP. App is VB6, same code on all platforms.|||I would update the MDAC on those machines and see if that fixes it. I have had that give me nightmares in the past.|||Will do... driver on XP seems newer that the 2000 machines already which is troubling. I have to travel over weekend, but will update this thread on Monday. Cheers!|||Cheers. :) Is it newer than what's on SQL Server? You are on the latest service pack correct? That would be 3a.|||SP3a confirmed.
SQL Server reports driver 2000.81.9042.00
XP Client also 2000.81.9042.00 - fails
2000 Client 2000.81.9002.00 - works
98 Client 2000.81.9001.40 - also works

I can't help but wonder if there's a setting outside of the ODBC properties on XP that is forcing a "Windows Auth-Only" connection. I don't know much about Local Security Policies but I may play around with that Monday. Meanwhile, members please feel free to offer suggestions :-)

Thanks