Can't do any changes to a job in SQL 2000
It sounds like you might be facing this issue ...

http://support.microsoft.com/kb/281642


  After the Windows server name been changed, when trying to update or
  delete the jobs previously created in a SQL Server 2000 instance, you
  may receive the following error message:
  
  Error 14274: Cannot add, update, or delete a job (or its steps or
  schedules) that originated from an MSX server. The job was not saved.


Here are the suggested steps to workaround the issue ...


  The best way to handle this problem after the rename process is to
  follow these steps:
  
  
  Rename the server back to the original name.
  Script out all of the jobs and then delete them.
  Rename the server to the new name.
  Add back the jobs by running the script generated from step 2.
  


Additionally you can find more discussion/suggestions here ...

http://blog.sqlauthority.com/2006/12/20/sql-server-fix-error-14274-cannot-add-update-or-delete-a-job-or-its-steps-or-schedules-that-originated-from-an-msx-server-the-job-was-not-saved/