Moodle 2.1.1+ - dataroot not writable

Hi,

I have a moodle installation that I need to setup to use a network share of the form \\root\moodle_data. 

I'm using IIS7.5 and moodle 2.1.1+ with PHP 5.3.8. I've given write permission to Everyone, IIS_IUSRS but nothing seems to work. 

I also tested it from a .net application and I was able to write to that directory.

Any ideas on what I could try ?

Thank you