OWA E2k3 stops working with 503 Service unavailable

Looking at the IIS logs this specifically is a 503 0 0 on the get verb on Exchange virtual directory

This KB helps here https://support.microsoft.com/kb/823159 

Found a couple of instances of needing HKCRScan and this finding a key that is problematic (contact MS support for this tool)

They typically start Nxxxxxxxxx

Perhaps put in by NetApp? At least ive seen them put in by NetApp