[SweetBearCub]

EDIT: Partial solution found. See post #7 of this thread.

Ok, so I finally got a generic screen protector on the phone while I wait for a real case and got it activated on my account.

I used Total Commander and went into HKLM\Comm\InternetSharing\ and deleted the value data for 'Extension'. (In other words, the key is still there, but it's blank.)

Then I went a level deeper, to \Settings. In there, I completely deleted the 'ForceCellConnection' key.

I waited 15 minuted, exited Total Commander, and turned the phone off and back on. When it came back up, the ForceCellConnection' key was back. The 'Extension' key was still blank.

I've tried this several times, no luck. I can get it temporarily working by deleting the key and launching Internet Sharing without rebooting the phone.

Any ideas to fix this?

In \Windows\Startup I did see a link for HTCStartup.lnk (I think that's what it was..)
Thinking that it might be some piece of HTC code such as HTC_CM_Guardian, I created a folder in the StartUp folder named Disabled and move the HTC link to it. Upon reboot, I got an error that the folder 'Disabled' was not signed and could not be executed. Good. But the registry changes still would not stick.