I have followed these instructions, and have Elements 10 on my machine, with the app correctly identified in Lightroom's preferences, but when I click on Edit in Elements, nothing happens - this is the case whether or not Elements has been launched.  Help????

Well, I've no doubt that it is supposed to work like that, but the fact is that it doesn't on my machine.  I'd have expected someone from Adobe to be responding, rather than another user, since, unless they've had the same problem they're unlikely to know what the solution might be. I should add that I'm using Lightroom 4, Elements 10 on an iMac, with the OSX Lion version 10.7.3 operating system.

I have the same problem with LR4 and elements 10 The popup says "Unexpected error performing command. Bad argument #1 'lower' (expected string, got nil).". i was going to buy LR4 but if it will not work with other adobe software i dont think I will be paying good money for it.

I have a problem, when Im done editing a photo in photoshop and swtitch back to lightroom, a new version of my edited photo DOES NOT appears next to the original, its at the end of my sequenced images, can you help me to set it back to appear next to the original?

How exactly do I do that?

I got it... after looking around I saw they were untitled, fixed it! Thanks for your help!

I had the problem and used chat to contact Adobe - very helpful.  Essentially you need to 1) remove your Lightroom preference file - it will have a .plist suffix, I think; 2) open Lightroom and click on 'Lightroom' on the menu strip; click on Preferences and then, when the box comes up, click on External Editing, move down to the Additional External Editor section and click on Choose, navigate to your Adobe Photoshop Elements Editor.app file and click on that - make sure you go to this file and not to Elements.app or Elements Organizer.app. Shut down Lightroom and open it up again, and it ought to work.  The preference file is regenerated when you open up Lightroom.