Why is it when I thread is moved...
 

I can no longer access it. Instead when I click on the link, the site returns:

Sorry, an error occurred. If you are unsure on how to use a feature, or don't know why you got this error message, try looking through the help files for more information.

The error returned was:

You do not have permission to view this topic

If the thread was moved to a section of the board you don't have access to, that's the error that is returned.