Print requests submitted to a print server might back up in the client system queue for the following reasons:
The print server is down.
The printer is disabled on the print server.
The network between the print client and print server is down.
Underlying network software was not set up properly.
While you are tracking the source of the problem, you should stop new requests from being added to the queue. See How to Accept or Reject Print Requests for a Printer for more information.