The SaveAs method is configured to require a rooted path, and the path <blah> is not rooted.
- by Jen
OK I've seen a few people with this issue - but I'm already using a file path, not a relative path.  My code works fine on my PC, but when another developer goes to upload an image they get this error.  I thought it was a security permission thing on the folder - but the system account has full access to the folder (though I get confused about how to test which account the application is running under).  Also usually running locally doesn't often give you too many security issues :) 
A code snippet:
        Guid fileIdentifier = Guid.NewGuid();
        CurrentUserInfo currentUser = CMSContext.CurrentUser;
        string identifier = currentUser.UserName.Replace(" ", "") + "_" + fileIdentifier.ToString();
        string fileName1 = System.IO.Path.GetFileName(fileUpload.PostedFile.FileName);
        string Name = System.IO.Path.GetFileNameWithoutExtension(fileName1);
        string renamedFile = fileName1.Replace(Name, identifier);
        string path = ConfigurationManager.AppSettings["MemberPhotoRepository"];
        String filenameToWriteTo = path + currentUser.UserName.Replace(" ", "") + fileName1;
        fileUpload.PostedFile.SaveAs(filenameToWriteTo);
Where my config settings value is:
Again this works fine on my PC!  (And I checked the other person has the folder on their PC).
Any suggestions would be appreciated - thanks :)