[Radiant] 500 errors in Admin after upgrade to 0.6.6

[Andy Ratike]

I have two Radiant sites that I setup a while back, with both Mongrel and
Nginx in front of them.  After upgrading to the 0.6.6 release today, the
sites are working fine, however, the admin interface throws 500 errors when
attempting to edit a page.  Has anyone else had this issue?  Any ideas as to
where I should start looking to debug this?  I'm green when it comes to
Rails...