Hello I guess you unpacked PSPad into new program files folder. No program has rights to write there! Please read instruction in developer forum - you should replace existing previous installation.
Copy content of previous PSPad into new folder (if you want to have PSPad in new folder) and than replace it with the current 5 version. You can start PSpad as admin, open program settings / System integration and check multiuser environment. Close PSpad and start is normally. But you will lack most of functionality, cause developer builds contains changed files only in compare to current full version. -- <http://forum.pspad.com/read.php?2,69155,69156> PSPad freeware editor http://www.pspad.com
