Hi sdayman,
There is no other security or caching plugin.
To be sure that no other plugin is disturbing I have disabled them and tried it again. No success!
I think you mean "wfcache" instead of "wpcache". After creating "wfcache" I changed the permission to 777.
The permission of that folder is still the same. Nothing changed.
Thanks
Edit:
Only one file "test.php" is created inside "wfache".
Thats all I can see there...