changing scheduled task user with same rights gives error result

Question

We are successfully running scheduled tasks on a windows 2003 server. The tasks are all executed batch files that are physically on a different server on the network. We use a domain admin user (so full rights) to run the tasks and to log on to servers.

Now we want to change the password of this admin user and we thought to finally create a specific user with the same domain admin rights, just to run those batch files on this and other servers in the domain. so the new user will have a hard to guess and never changing password. the old user will regularly change it's password from now on.

Problem is : if I change the user of the scheduled tasks from domain admin A to domain admin B, those tasks are failing (0x1), although the users have the same rights. the B user can access all network places. the server is logged on with user A, but the batch files should be executed with user B.

Anyone that recognizes the problem?