[TYPO3] Problem when uploading files: Your login has probably expired

[Vincent Mans]

Hi List,

In one install I have strange problems:


   - When I upload a file (picture), a JavaScript warning appears:"Your
   login has probably expired. Do you want to refresh it now?". If I click
   "cancel", the upload continues
   - Next to the field for file upload, the button is missing; only the
   alt-text is visible: "Browse for files". If I use a skin for the backend,
   many buttons disappear

These problems

   - appeared suddenly and not after installing an extension
   - appear in Firefox and IE, both latest versions
   - existed when version was 3.8
   - still exist after upgrading to 4.0.2
   - exist for all beusers
   - local; on the server more installs are done in version 3.8 en the
   4-series; no problems there

So it looks like the problem lies somewhere in the typo3conf but I have no
further clue.

This type of question has been asked earlier in the list, but not answered.
Hopefully there is more experience now ;-)

Kind regards,
Vincent