XF 1.5 Permissions Error

[DVUnderground]

I keep getting 'You do not have permission to view this page or perform this action.'
I can see the forum fine when I'm not logged in but as soon as I log in i get the permission error. I've double and triple checked all my User Group Permissions and Node Permissions and they are turned on.

The error I keep seeing in my logs is:

ErrorException: Fatal Error: Class name must be a valid object or a string - library/XenForo/Model/Node.php:521
Generated By: Unknown Account, 1 minute ago
Stack Trace
#0 [internal function]: XenForo_Application::handleFatalError()
#1 {main}
Request State
array(3) {
["url"] => string(31) "http://forum.dvunderground.com/"
["_GET"] => array(0) {
}
["_POST"] => array(0) {
}
}

 

[M@rc]

I get this error when I try to access the forum :

"forum.dvunderground.com is currently unable to handle this request."

 

[DVUnderground]

I get this error when I try to access the forum :

"forum.dvunderground.com is currently unable to handle this request."

Try http://forum.dvunderground.com/forums/dvu.2/

 

[Paul B]

To reiterate what I said in the ticket.

You can use the permissions analyzer to determine where and how the final value is being set.

These guides should help:
https://xenforo.com/community/resources/implementing-permissions-across-multiple-user-groups.358/
https://xenforo.com/community/resources/understanding-permissions.360/

Can you post the full contents of the error including the title and stack trace.