yay! it worked! thank you 

I have even tried uploading the newest "original" filemanager (you know without localization), but no difference :S

They really weird thing though, is that it did work once, I have really no idea what happened, even a completely fresh upload doesn't work.. (Do you perhaps have an older version to try?)

I don't know whether it matters, but it is running on a Windows server 2008 with IIS (7 or 7.5).

Though since it's only the treeview which doesn't work, I guess it shouldn't matter.. It can't be a problem with permissions or anything, because as mentioned the gridview and everything else does work..

Hope you aren't as clueless as I currently am 

Though thanks in advance :)

.. Good idea to use firebug to track down the error, why didn't I think of that.. Can't count how many things I have tried to make it work..

Well my problem was that I had a rule on my website, that it automatically make the URL in lowercase so if you goto MyPage.html it would automatically correct it to mypage.html (in favor for the Search Engines, since MyPage.html and mypage.html isn't the same page in their eyes..)

Anyhow some files where called MyTreeView (for instance) and when that was auto corrected it couldn't find some files (e.g. MyTreeView.js). In my opinion though, that doesn't make any sense, since the server shouldn't be case-sensitive.. ?

When I disable the rule, everything works perfectly, so I'll try to locate every place which uses uppercases at lowercase them :)

Once again, thank you for take the time.. 

**UPDATE**

If it should be in any interest to edit this (no really reason to use uppercase?), I found the relative few places where uppercase are used..

File names:
\scripts\jquery.filetree\jqueryfiletree.css

\scripts\jquery.filetree\jqueryfiletree.js

\scripts\jquery.filetree\connectors\jqueryfiletree.php (all of them)

\scripts\jquery.contextmenu\jquery.contextmenu.css

\index.html (if you use .net you could with advantage rename it to index.aspx and you will be able to use the build in safety features..)

Line 41,42 to:

\scripts\filemanager.js

Line 6 to:
      var treeConnector = 'scripts/jquery.filetree/connectors/jqueryfiletree.' + lang;