That's correct and been reported to WA a couple of times.
You could simply remove the head regions like
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
form the plugin page.
I'm not sure if this gets fixed in an upcoming update to FB or Design Extender, however that has never been a problem to the pages I've made with FB.
I've looked at your page and can only assume, that the code for either DMX calendar or PowerGallery should be moved somewhere else in the source. I've had similar issues with extensions and DWT.-based pages and got them resolved by moving code blocks. Not sure, however, if that's the case with your page.
And, at least for me, that was always some kind of trial-and-error.
so be sure to make copies of your pages.
Another reason might be, that you are possibly referencing two jQuery libraries (just a thought, I'm not sure at all!):
(That's the DMX version)
(That's the one form Power Gallery, I guess)
Like I said, not sure, if that's the reason, but you could try to comment that google-code out for testing.