I just switched from T-Mobile to AT&T, and for some reason had no data connection on the phone, even with the correct APN settings. I decided to try a factory reset. I went through the system settings menu and found the "Reset to factory settings" menu item, selected it, acknowledged the warning, input my PIN and let it go to work.
A few minutes later, it had rebooted into recovery. Sicne it was there, I took the opportunity to use the boot-loader's reset function and wiped the cache while I was at it. That was a mistake.
Now, the phone won't boot past the pulsing Samsung logo. I can get back to the recovery, and it pops up these errors - first, the droid on his back with the red triangle over him flashes "No command", and then it dumps me to the recovery menu with this scrolled at the bottom of the screen:
# MANUAL MODE # -- Appling Multi-CSC... Applied the CSC-code : TMB Successfully applied multi-CSC E:failed to mount /data (Invalid argument) can't mount '/data' (Invalid argument) E:failed to mount /data (Invalid argument) E:Can't mount /data/log/recovery_log.txt
edit to add:
I've already tried the stock UVUEMJC firmware from DocHoliday77's thread, but it threw a bunch of errors across the screen that I didn't catch in time and rebooted to the same point.