If the registry is unresponsive, you will now get an error
specific to this, rather than a misleading "provider unavailable" type
error. Also adds debug logging for when errors like this may occur
Some errors from Get are essentially user error, so we want to be able to
recognize them and give the user good feedback on how to proceed.
Although sentinel values are not an ideal solution to this, it's something
reasonably simple we can do to get this done without lots of refactoring.
Pam Selle