Problem:
When installing a networked printer you receive a The Specified Print Monitor is Unknown error.

Solution:
1.) Enable UAC (Go into the control panel and type UAC in the search bar then follow through the 'wizard') -- restart your computer when prompted
2.) Install the printer
3.) Disable UAC

Source: http://vistafix.blogspot.com/2006/12/installing-networked-printers-specified.html