I recently came across a page that was giving me this error:
The control type '...' is not allowed on this page. The type is not registered as safe.
The obvious solution is to add a <SafeControl> tag to the web.config, but checking with my developer, he said it was not necessary and he does not have that declaration on his test server.
This led me to hypothesize that a custom branding we had was causing the problem to which my developer corroborated that unghosted master pages will cause problems.
So how to locate the unghosted pages? This led me to the following post: Ghosts in the Machine? However, this is for SharePoint 2007 so taking a leap of faith, I modified the SQL script provided and came up with this:
SELECT TOP 1000
where ([AllDocs].[Type] = 0)
AND ([AllDocs].SetupPath IS NOT NULL)
AND ([AllDocs].DocFlags & 64 = 64)
Checking the reference for the AllDocs Table this query seemed to make sense.