The requested page cannot be accessed because the related configuration data for the page is invalid.
Most likely causes: •The worker process is unable to read the applicationhost.config or web.config file. •There is malformed XML in the applicationhost.config or web.config file. •The server cannot access the applicationhost.config or web.config file because of incorrect NTFS permissions.
Things you can try: •Look in the event logs for information about why the configuration files are not readable. •Make sure the user identity specified for the application pool, or the authenticated user, has the required permissions to access the web.config file.
An Update (possibly WSUS) or installation other inserted a line into ApplicationHost.config when it registered its WSUS x64 DLL-- which turned on Dynamic Compression (as opposed to Static Compression which is probably already enabled), or an update was run that did not complete or clean up after its self. In this case the following section was added to "C:\Windows\System32\inetsrv\ApplicationHost.config". The path to the compression DLL existed, but file did not.