Note to self:
Server Error in '/AppName' Application.
Login failed for user 'db_reader'. Reason: Not associated with a trusted SQL Server connection.
When you install MSDE2000a and specify mixed mode authentication during setup it does not remember your choice. You have to go in manually:
SQL Server Enterprise Manager -> Console Root - > Microsoft SQL Servers -> SQL Server Group -> Properties -> Security Tab. Verify that the authentication mode is "SQL Server and Windows".
Just a minor annoyance, but I figured I might save someone the 5 minutes if they ever run into it.