Error "failed to delete index.php"

[softfocus_marketing]

When I make changes to a Product Category in VirtueMart, I am getting the Error "failed to delete index.html", it is however saving the simple html changes in the backend. I figure it must be a permissions thing but haven't been able to find it. We also tested this on our development server and it worked fine.
The site is in Joomla 2.5.9.