Cross-Domain Receiver Error - Ensure callback URL is correct

I'm glad you got it figured out. Thanks for posting back your solution.

As for the button not showing up in IE, do you happen to get any Javascript errors or anything when that happens? Is it when you do CTRL+R to reload the page or anything? I'm wondering if it's a caching issue. If you have access to your apache logs, I would watch them to see if you can see the image being requested and if it seems like apache is sending it back or maybe having issues.

Let me know if you want help figuring it out.