iPhoto freezes when changing editor in Pref.

I use iPhoto with PSE8 as external editor for at least 3 years and never had any problem.
Today I installed the new PSE11, maybe it has something to do with the problem.
I wanted to change the external editor from PSE8 to PSE11.
The moment I clicked on PSE8 in "use editor" in Advanced tab in Pref., iPhoto froze.
I unsynced MobileMe in system pref., removed it from upper bar, repaired permissions, iPhoto database...
iPhoto opens as usual in PSE8 for editing, but trying to switch editors in Pref. causes lockup.
What should I do please ?