Why does my Server 2008 R2 print spooler keep stopping?

I have a print server running on a VM using Server 2008 R2. The clients ar all HP Dc7900s, with Office 2010. They are printing to an HP4014n, as well as a RICOH 6001. More than occasionally, the printers read offline. If I go into the services on the individual client and restart the spooler then the printers come online. Why does the spooler keep stopping and how can I prenvent it from happening so often?