The same Runtime Error occurred for me again yesterday.
I tried all sorts of approaches including Windows System Restore, checking that no Windows Updates had occurred, and then I tried Uninstall and Reinstall of PSP X5, as well as the Repair option.
None of these worked for me so I did an Uninstall again and ran the utility PSPX5_Cleanup.exe before Reinstalling.
According to the log, this did the following:
Force to uninstall all modules... (MSI)
Remove PaintShop Pro folder...
Remove registry data...
After this PSP X5 works but I lost all my Registry settings (the same as doing a Shift+PSPX5). I did restore my Workspace successfully.
I find it very worrying that one can lose the PSP Program so easily for no apparent reason