Ok heres what you do. First try and kill process: asrunjob.exe.
If this doesnt work, then stop the job engine, open the Arcserve folder, go into the 00001.QSD folder. Referring to the job ID, delete the .CHK file relating to the hung job, create a folder called TEMP and move the other job file (same number) into this temp folder.
Delete the file called QSYS.QUF (NOT QJF).
Start the job engine, the job will be removed from the queue, which you can add later.
If its backing up a remote server via client agent, stop start the agent to cancel the connection.
Hope this helps.