I get the error "The print processor is unknown" when installing a printer.

The default print processor winprint.dll is missing from the directory %systemroot%system32SpoolPrtprocsW32x86

The Winprint key in the registry is missing or corrupt

Start the registry editor (regedit.exe)

Move to HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlPrintEnvironmentsWindows NT x86Print Processors

If the winprint key exists goto step 4. If it does not exist from the Edit menu, select New -Key, and enter a name of winprint

Under winprint check for a value called Driver. If this does not exist from the Edit menu, select New - String Value and enter a name of Driver.

Driver should have a value of winprint.dll. If it does not, double click on Driver and set to winprint.dll. Click OK

Close the registry editor

You should now restart the computer