I've had my X for about two years now and it started exhibiting the camera error symptom a couple of days ago.
I've done exhaustive research over several Forums, including this one and the "official" HTC Forums - all to no avail.
I've reset my phone to factory defaults a couple times, tried installing other camera apps, etc. Still, nothing "permanently" worked. The camera would boot up, and then crash immediately.
So, after ordering a new HTC One (M8), I spent some time with the X to try everything I could, no matter what it was.
This is what worked for me:
- I sent all my pics to Google Drive, and made sure everything was synced
- I removed my SIM card (no instructions I read in any Forum stated to do this)
- I reset the phone to factory default
- When it cycled through the erasure of data and rebooted, I skipped the Google sign-in procedure (including choosing a WiFi network) and got the phone settled to "Emergency Calls Only" (DO NOT CHOOSE THAT OPTION IN THE SIGN-UP PROCEDURE - ALWAYS CHOOSE "SKIP")
- Then, I inserted my SIM card, and waited a few seconds to handshake with my carrier's network.
I didn't have to fool with disabling anything, and all features worked - even the camera and another downloaded app - Camera FV-5 (which is awesome, BTW).
Once I confirmed things were back to normal, I went to the PlayStore and downloaded all my apps.
Yep, still working!!!
I've been assembling and troubleshooting PC's for almost 20 years and this is one of the first times that I have come across a unique fix to a very common problem on any device I've seen.
Hope this works for you, too!