Try the troubleshooting steps here: http://helpx.adobe.com/x-productkb/multi/edit-photoshop-command-missin g-photoshop.html
OK I am in the same boat. I have a Mac. The problem exists from a fresh install of Lightroom 4 and Elements 10. Tried rebuilding the plist file, though why that would work is beyond me. Have uninstalled both and reinstalled them.
Is there anyone with Lightroom 4 and Elements 10 on a Mac that actually have them integrated properly (and I dont mean by using the external editor option)
I am running an iMac Core2 Duo 2.4ghz processor, Snow Leopard 10.6.8, LR4.1 and PS Elements 10.0, and I just was able to open in Elements a Tiff generated in LR using the "Edit In..." option from Photo menu.
Europe, Middle East and Africa