I assume that you are using Remote Desktop Services for the client computers. What OS/version are the clients using?

Possibly useful links, in case you haven't already seen them:

http://serverfault.com/questions/523...012-cant-print

http://serverfault.com/questions/650...-r2-rds-server

http://theitbros.com/easy-print-windows-server-2012/

https://technet.microsoft.com/en-us/...(v=ws.11).aspx

http://searchvirtualdesktop.techtarg...roblems-in-RDS
(This one wants an e-mail address to view the full article.)

http://arstechnica.com/civis/viewtopic.php?t=1234053