Be warned, this will void your warranty, and could render your phone useless / bricked. Continue at your own peril.
After you have downloaded the Android SDK, open a shell and navigate to the "platform-tools" directory. It contains an executable called "fastboot" that we will use later on.
First we have to boot the phone into the bootloader. This is done by holding down the power button and the volume up button when the phone is starting.
When you are presented with an old school menu, scroll to "Fastboot" using the volume up/down keys, and select it with the power button.
Your phone is now in fastboot mode.
From your shell, type in "sudo ./fastboot oem get_identifier_token." You should get a long string of text. This is your unique token. Save it for later.
Now go to "http://www.htcdev.com/" and select "Unlock Bootloader." In the dropdown, select "All Other Supported Devices." You can skip all of this until you reach the input box where you should paste in the token you saved in the last step. If you get a failure, read the instructions on the HTC webpage that explains very detailed what the token should look like.
You should receive an email from HTC with an attachment, "Unlock_code.bin" in my case. Download the attachment and put it in the /tmp directory.
In your shell, type in "sudo ./fastboot flash unlocktoken /tmp/Unlock_code.bin" which should prompt you on the phone if you want to unlock the bootloader.
Select "Yes" and press the power button. Your phone will now reboot, and your bootloader is now unlocked.
I had a problem where the Garmin ANT Agent would connect to my Forerunner 910XT and try and sync up with new activities, only to discover that it would fail with "Downloading fitness data failed" error message.
I scourged the internet high and low to find a solution, but most of them involved resetting my watch to factory defaults. Which I did not want.
After a while, I found a recipe for enabling debugging on a Mac here. But this did not help me, as I am using a Windows 7 machine.
So fiddling a bit about, I managed to get debugging up and running by doing these steps:
Click "Start Menu" and type in "regedit.exe"
Go to "HKEY_CURRENT_USER\Software\Garmin\Garmin ANT Agent(tm)\Settings"
Create a new entry of type "Binary Value" with the name "ShowDebug"
Set the value to "01"
It should look something like this:
Now restart your ANT Agent and there should be loads of debug files located in the folder C:\Users\mattis\AppData\Local\Temp\ANTAgent\
"Unfortunately", right after I enabled debugging, the problem fixed itself, so I never had to actually analyze the logs.