Several users have reported an issue in which Photoshop CS5 and other Adobe CS5 apps crash when opening documents created in CS4 applications, as well as other problematic documents. As described by a poster to Adobe’s support forums, Todd Clary:
“Suddenly Photoshop CS5 refuses to open any document created and/or saved in Photoshop CS4. It works if I create a brand new document in CS5 but crashes every time I try to open anything I’d created in CS4.”
It appears that, in at least some cases, this problem is due to one or more font issues. In some cases, deactivating Extensis Suitcase 2 can resolve the issue. In extreme cases, you may need to uninstall Suitcase altogether and load all fonts directly through the standard Mac OS X framework.