Exchange Virtual HTTP Server Error

Hi All. I have a problem with my exchange server. we run outlook web access from the server and the HTTP virtual server has been stopped. when i try to restart it i get the following error

Cannot create a file when that file already exists
Faciltiy: Win32
ID no: 800700b7
Exchange system manager

Has anyone come accross this already, if so how do I get around it?
any ideas would be really helpful.
Thanks