I'm sure I came across this--I've been reading mixed comments from people at the discussions about this issue---my old computer decided to die out on me June 22nd--only recently did I get a new computer and of course it has Mountain Lion....I have a i800 Microtek photoscanner which came with PhotoShop Elements but version 4 as my old computer was still running on Tiger edition--to put it mildly there is no way I could budget the regular Photoshop which costs a hefty $699.00 while PhotoElements goes for about $99.00----
I just loaded my actions int the PSE 10 purchased from the App Store.
Access the System library location from Finder menu, click "Go" in the menu bar then select "Go to Folder...". Type in "~/Library" and click Go.
The systems Library will open up and then you take this path:
Application Support > Adobe > Adobe Photoshop Elements 10 Editor > Presets > Actions (The Actions folder is where you move your actions file to)
Then go to the Photo Creations Folder > Locales > en_US and delete the MediaDatabase.db3 file (move it to the trash)
The next time you launch PSE your Actions DB will be rebuilt with the new actions installed.