Need URGENT help

[New Joe]

Go to Settings, then to Navigation Manager.
Click on edit for the Forums tab
The : Target URL
is where forum.php is, this is what is throwing the error when you click on the Forums tab on your forum

Target URL
This is the URL that the Tab or Link should redirect you to. It can be a relative target or a full url. It can also be blank (sometimes useful for tabs, not really useful for links).

Try leaving it blank or putting in your url

--------------- Added [DATE]1343489712[/DATE] at [TIME]1343489712[/TIME] ---------------

Did that work?

--------------- Added [DATE]1343489825[/DATE] at [TIME]1343489825[/TIME] ---------------

I see your site it now changed back to the default /forum.php

It was fine as you had it before, you just needed to alter what I posted above