If you have a Sprint HTC Arrive Windows Phone 7 and you can’t get the developer registration tool to work, then here’s your solution.

I found this after a lot of searching on the MSDN forums:

HTC Arrive configuration issue.

Try this:

1. if connected, unplug the phone device from the computer.
   _on the phone_:
2. Press the Windows button.
3. Press the right arrow button, or swipe left, to expose application list.
4. Select “Settings” option from the application list.
5. Select “Cellular” option in the settings list.
6. Select “Change Network Profile” and wait for this operation to complete. (This is a key step! However, you don’t need to actually change anything on the resulting page.)
7. Press the back button or Windows key to exit the Settings application.
8. Retry the phone registration process.

This worked like a charm for me and I’m sharing it here to save other the hassles I went through.

As far as I can tell this only applies the HTC Arrive phone.