When trying to install a shared network printer in Windows Vista, you get an error which states:
Windows cannot connect to the printer.
The specified print monitor is unknown.
This is a bug in Vista. If you disable the UAC, Vista is seemingly unable to add a network printer.
To fix this, you’ll need to install a “Performance and Reliability Update”, KB938979. Bizarrely, this update is listed as Optional by Windows Update, and so you may not have installed it. I shall refrain from commenting further on the lunacy of this 😉