Backend products not editable

[t-cue]

Hi there,

I've got a problem. When i try to edit products or catagories in the backend i get a page with no layout and just the menu of virtuemart in the left like it's a plain HTML page. So, i can't edit my products anymore. Does someone know what's going wrong? I tried several things. Update VM, overwrite through ftp, cleane cache, turn of Akeeba Admin Tools, other backend template, restore backups from the time it worked. Nothing works.
Thanks in advance. It dit work, but al of the sudden it's gone.

Joomla: 2.5.14
VM: 2.0.24
PHP: 5.4.21

Best regards,

Erik.

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