After reading hundreds of posts and trying EVERYTHING by "THE LETTER"! I finally stumbled upon a solution (for me at least)...
I upgraded from a perfectly working version only to be confronted with the "LOADING" message. I edit the .js files, re-installed, and everything else this thread recommended doing.
I'm running vbulletin off of my root and vBA.
My Solution may or may not work for you but it won't damage anything to try...
Copy the clientscript directory in the .zip file into your root.
For example...
www.yoursitename.com/clientscript >>>>Copied to here.
www.yoursitename.com/forums/clientscript
I'm running the "forums" version. So I copied the clientscript dir to the root and voila. Not the cleanest but I searched high and low for a reference to the php file within all of the files in the script to change the path but could not find it.
It's working now and I'm happy.