IO Exception access folder

I had my file vista site running fine on my customers ISP.  Then a week later I am getting

System.io.DirectoryNotFoundException - Attempting to access a path that is not on disk

At first I thought maybe this is a permissions problem, so I worked with my ISP and they asked for an ID to test it out with.  I created them an ID in fileVista and assigned it to one of the root folders (I can still get in the application, just jump past the error, but I dotn have any folders)  I tested the ID for them that I just created and VOILA - that id can see all the root folders that I assign to it.  

So I am very confused, my theory of filesystem permission is out the window.. why would all my userid loose access to the folders and any new ids have access?

Thanks in advance for any information

It seems the path that your root folder pointed to, was deleted. So it's not a permissions issue. When you open the root folder properties and click Ok regardless of adding a new user or not, the existence of the path is checked and recreated if it doesn't exist. You didn't receive an error with the new user because the folder was recreated when you modified the root folder.

Just save all of your root folders so that the paths are recreated. You need to find why the folders were suddenly deleted though.