I have just uninstalled and reinstalled PSPX3 due to plug-in problems. I cannot add file locations because there is no OK/Cancel/Help button on the bottom of the box???
I have used PSP since version 9, and this is the first time that this has occured.
What patches have you installed? It seems that the 3rd Service pack seems to have caused more problems than it fixes. If you did install SP3, try completely uninstalling it again, and this time when you re-install before installing any of the updates, launch PSP X3 to see if the problem persists. If not, install the first update, and check again. If it's still ok, install the 2nd one. If it is still ok, and you don't have any problems, I'd leave it there.
FWIW, I'm not running Win7, but I have jumped over the 3rd update and only have SP1,2, & 4 installed. I still get a nag screen about an update but I choose to ignore it.
I wonder if it's specific to PSP. It could be but there are similar dialog is other places.
Have you tried hitting "Enter" after selecting your folder? It should default to the OK button even if the button is not visible on the dialog the button should still technically exist.