Print Queues failing to clear

We are running an NT 4.0 server and are having problems with our print queues. it started with Apple 8500 print queues but occasionally affects Hp 4050 q’s.

The print job will reach the print queue and sometime print but not clear, sometimes not print, just sit there, and other times look like it is going to print (Flashing light on Printer) but nothing happens. we then get a timeout error message…i ahve adjusted the timeout values both to increase and decrease, but this seems to have no effect.

Any suggestions would be appreciated.
Darren