[TheLastSuperman]

Maxii,

You did upload the new "licensed" files over the old ones correct? This could be causing a issue and tbo you never know what's been "included" in a nulled version so you could have a security risk or two which I'm not trying to scare you but also state that for others as well - it's not well advised to run a illegal version for that very reason amongst many others.

Be sure you've uploaded all the new files from the .zip you downloaded form the members area, be sure to download the same exact version unless your upgrading here are some steps:

If your on 4.1.5 for example:
1) Download a fresh copy of the 4.1.5.zip from members.vbulletin.com
2) Be sure to edit config.php.new and rename to config.php then edit and copy over all your database details and more from the old config.php into the new config.php before overwriting.
3) Remove the install.php from the install folder (your only upgrading not installing and you'll need to remove it before accessing the admincp after the upgrade so don't bother uploading it, skip it ) and also removed the favicon.ico if you have a custom one already within the root folder etc.
4) Upload all the new files over your existing ones, this now replaces your old "nulled" files with legally licensed files that contain your correct license #.

Now refresh the site, create a new default style and see if that sorted the issue?
If NO then you can try one more step:
5) Run the upgrade script, bearing in mind your not upgrading however this may run through the motions and reset a few things the illegal version mucked up per say.
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Now if that does not do the trick you can try the same as above except you can snag the newest version and upgrade to see if that will help sort it otherwise you may need to ask for support via the ticket system or in the off chance you can't sort it hire someone who can although I hope the information posted helps and your able to get going, since you finally joined the rest of us in the land of licensed .