wipes out Lightbox when the new jQuery object is re-created (for a 3rd time). The 3 script references in your HTML look like this:
The first one is probably automatically injected, so I would leave that. The other 2 are probably in in the site.cshtml file of the AllTuts theme. I would remove those bottom two.
.... back to the Contact page error. If you haven't yet, two changes I would try making to the web.config file are.
#1, Change the <customErrors> tag so the mode is Off (case sensitive), as in:
#2, Change the debug attribute on the <compilation> tag to true, as in:
<compilation debug="true" targetFramework="4.0">
These two changes might make it so some error details are revealed in the response from the server. You might need to monitor the response coming back from the server via Fiddler or Firebug, if you are
not doing so already.