I'm pretty much in the same boat as a few others here - except I know exactly where I went wrong and learned a valuable lesson.....
Before I started all this, I had S-OFF, Root and running ViperOne on my M8
Wanted to try out a AOSP Rom and used a 4.4.3 GPE ROM, which flashed successfully (not sure how, it shouldn't have).
Once the M8 was running 4.4.3 GPE, it prompted for an update to 4.4.4 which I accepted. The update failed and booted into TWRP instead. I was overly determined to get 4.4.4 installed (should have left it alone at this point instead)
I rebooted into bootloader and very very stupidly, flashed the GPE recovery, rebooted and accepted the install to 4.4.4.
This boot looped my phone, corrupted internal storage, and reapplied security (S-On).
I was able to get internal storage cleared up and successfully installed CM11 so at least I'm booting something and its not bricked.
At this point, I'm back to a bootable state with CM11 - but can't return to Sense. I've tried to install InsertCoin and ViperOne - both fail towards the end of installation - writing permissions and installing busybox - same with restoring ROM via recovery. Also, the original GPE ROM fails installation, but doesn't give any errors.
I've tried to S-Off with revone, firewater, SunShine and rumrunner - all fail. I need S-Off to get HBoot back to a version that can boot Sense or open up security so a Sense based ROM can install successfully. Also tried to SuperCID, which requires S-OFF so that fails as well.
So I'm stuck with:
- S-On
- version-bootloader: 3.18.0.0000
- version-baseband: 1.14.21331931.LA02_2G
- modelid: 0P6B13000
- cidnum: T-MOB010
I've tried flashing current (and previous versions) stock Firmware and using different versions of RUU but all fail with hboot version check failed and S-On. Flashing GPE 4.4.x (4.4.3 and 4.4.4) firmware fail as well but cant remember the exact error off the top of my head.
I'm at a loss.. Over the years I've read plenty of tutorials and have a pretty decent understanding of the Android ROM ecosystem. I've searched all over to no avail. If the GPE Recovery and/or 4.4.4 Update would have left Security Off, I wouldn't have any issues since I could flash firmware or HBoot and install ViperOne or any other Sense based ROMs....
I've been racking my brain trying to fix this for 2 days now so I've come here for a bit of help... I've tried to list all my troubleshooting steps in here, but I know I've missed some
Any ideas?? One thing that would really come in handy right now is one of the several S-Off methods to work on AOSP Roms.