I didn't disable anything else, but didn't go fully through the login process, so maybe I missed that. I just tried right now though, and I registered without problems. I then logged out, and then re-logged in and was properly redirected back to the home page. So that seems to be working for me.
I'm not sure why the page broke recently, and am still not 100% certain why it's breaking in IE right now. I have suggested a few problems, but can take you through why I've thought it was this or that. It all boils down to a Javascript error reported in IE that says "this.el does not exist" (or something similar). It was a vague error that was hard to track down, because IE doesn't always denote which file is causing the error.
* At first, I suggested the template, because there were multiple versions of Mootools being loaded, which has definitely been known to cause problems in the past. This double-inclusion was done by your template, but only because it was using a module for menus called at_menu
* Then, I got into the site, and disabled the ARI menu modules, and realized it was working better.
* So, I looked further into what that module includes and found the Ext javascript library, which, when looking through the code found references to this.el. I still don't know what it's doing wrong, but that's the line throwing the error.
So, yes, a few wrong paths, but things seem good on your site now (albeit without menus you probably want).
As for Rockettheme templates, yes, there's quite a few sites that work with JFBConnect and their templates. The only problems we've had in the past is with their RokBox module, which can load a pop-up of the JFBCLogin module that has the Login With Facebook button missing. We have a simple workaround for that now in our Common Support Questions area, which we can help you with should you want to use the login pop-up.
Hope that helps explain the thought process, and hope we get you all fixed up soon!
Alex
Facebook login not working in IE8
