If you have once run PSE it is necessary to also delete the saved application states.
So you would need to delete:
com.adobe.PhotoshopElements.plist
Adobe Photoshop Elements < version > Paths
Adobe Photoshop Elements < version > Settings
com.adobe.Elements Organizer. < version >.plist
com.adobe.ElementsOrganizer< version>.plist
and any lockfiles with the same names, then go to Saved Application States (at the same level as preferences) and delete any for PSE, then repair permissions and try again.
However, I will say that I am not running Yosemite (and don't intend to any time soon), but from the folks I knew who were in the Apple beta, it breaks many, many existing programs.