For anyone that gets the no permission error and you've already set your permissions in admincp, you might be having the same problem I had in the past. If you are using an editor such as Dreamweaver to edit your files, this is most likely the problem. Redo the modifications to your global.php file using notepad to edit it and this should fix it...well at least it fixed mine and it was definitely the global.php.
I just went through this exact problem again since I updated my vbulletin to 3.04. :squareeyed:
Hopefully this may help a few others here having the same problem.