Found this on HTC's website
Performing a factory reset using phone buttons
If you cannot turn on your phone or access the phone settings, you can still perform a factory reset by using the buttons on the phone.
With the phone turned off, press and hold the VOLUME DOWN button, and then briefly press the POWER button.
Note: If you are not sure whether your phone's power is turned off, remove and then reinsert the battery.
Wait for the screen with the three Android images to appear, and then release the VOLUME DOWN button.
Press VOLUME DOWN to select CLEAR STORAGE, and then press POWER.
Press VOLUME UP to start the factory reset.
Is that what you are doing to get to the error screen you are currently getting?