"Data Call Failure" Error 67 - Solution #1

Beware people (like me) who offer solutions (like this)...

That said, here is how I have (several times) repaired this error on my HTC EVO 4G LTE.
(it's a Sprint phone, but I think these issues are across all of the telcos)

On your KEYPAD, type this:

##72786#

It will switch to a special mode with "SCRTN" as the Header.

Select the "Menu" button at top right of your screen, two options will appear:

Reset or Cancel

Select Reset
Stuff will happen automagically, and the phone will reboot. Cross your fingers & toes, and if you got it right, the phone will come up, and that error message will be all gone away...