Rename Admin account in Win2k Server

First some advice:
NEVER, ever give the administrator account a blank password unless: 1. You never intend on connecting to the Internet; and 2. Either you are the only one with either physical or network access to this server, or you TOTALLY trust ALL your users, or you have absolutely NOTHING of value on the server (to include your time and energy in setting it up).

Now to answer your specific question:

The reason this is happening is that the backup job (I'm assuming it's set to run on a schedule vs. a single time) was setup to run under the context of a specific set of user credentials (in your case, probably Administrator). Everytime the backup engine starts it searches for this set of credentials to see if they are still valid. Since you changed the name of the administrator account, the backup engine determines that the set of credentials originally supplied are no longer valid and the backup job aborts.

To fix this, you really only have one option (regardless of whether you change the account name back to administrator or not). You need to delete the backup job and recreate it supplying a valid set of credentials when asked during the setup process. The credentials can either be for Administrator account (if you change the name back), the NAME account (if you choose not to try and rename the account), or some other account that has the permissions necessary to run a backup.