Hi,
If u installed via autoinstaller like Fantastico or someting.. try reinstalled manually, download from www.remarpro.com then upload to webhost.
I tried on my newly wordpress site via fantastico and giving me same error like you received. Tried delete /upgrade and recreate and its only work for a while.
I delete everything and installed manually, no problem there after..
its indeed a prob with permission like some of u explained before…