Thanks for the comment, Lisa.
My last post wasn't clear about the timing of the upgrade, but I tried upgrading after I saw that ImageMagick wasn't working properly. Upgrading didn't solve the problem
For time being, I decided to use GD for image processing instead, and it works all right.
Is there any chance ImageMagick installation isn't appropriately done on a particular server?
Anyway, I'll check the perms and for corrupt files.
Thank you.
yoshi