Is there pspshellx64.dll in PSPad folder? If yes, go to program settings / System and choose DLL (not registry) way and check option you want to have in context menu. If the options is checked, uncheck it, check it again and confirm.
The shell DLL what is installed depends of your system (32 or 64 bit) -- <http://forum.pspad.com/read.php?6,62973,63019> PSPad freeware editor http://www.pspad.com
