Using the Oracle Data Provider for .NET, my application connects to the database using the privileged SYS user. The connection string is as follows:

Data Source=MyTnsName;User ID=sys;Password=MySysPassword;DBA Privilege=SYSDBA

This works fine with Oracle 10, but Oracle 11 keeps complaining about an invalid username or password. I verified that the password is correct - other apps work fine with the same credentials.

Note that for regular users (without the DBA Privilege part), connecting to Oracle 11 works perfectly.

So, what's wrong?

Update:
This is not an issue with case sensitivity - when constructing the connection string, the password case is not altered by my code, and the password works fine with other, non-.NET-applications.

I suspect that this might be caused by the Oracle 10 client I'm using to connect to the 11 database. Oracle states that the client is upward-compatible, the only drawback being that you cannot use some new features of the database. However, SYSDBA connections clearly are not a new Oracle 11 feature, and - again - a non-.NET-app (Keeptool Hora) can connect using the same setup.

Any other ideas?

Update 2:
The problem persists when using an Oracle 11 client :-(