Exchange OWA not working

Hi,

I hope someone can shed a little light on an issue with have with an exchange 2007 server. When we try and get to the OWA webpage we get an error. Server error in '/owa' Application. Web.config Configuration File

We have deleted and rebuild the virtual directorys, patched the box to current highest levels. It will not load the logon page nor does outlook anywhere work

Any suggestions

Many thanks