A PostScript error undefined, offending command pR can occur when printing from Netscape Navigator with the Microsoft Windows PostScript printer driver. Some releases of Netscape don’t do this.
You can get around this problem by using the Adobe PostScript driver (AdobePS), and by downloading the following patch file to the printer (this fix will remain active until you reset or reboot your RIP or printer).
serverdict begin 0 exitserver
/pR 0 def /pG 0 def /pB 0 def
Instead of downloading the above code to the RIP you can also add the third (and only the third) line above to the existing PostScript printfile.