I had a modded 360 with 1.41 firmware. Today, I tried to update it to 1.51 using JungleFlasher. I was having problems with the computer recognizing the drive, but I finally got it to see it.
I clicked Erase under the MTK Flash 32 tab, the my PC froze. Had to reboot, then my 360's DVD drive wouldn't open. Awhile later, I got it to open, then I proceeded to continue.
I loaded up 1.51 then Read the firmware, then I erased it, then I clicked Write and then it wrote it.
And now, I get "to play this disc, put it in an xbox 360 console" whenever I try to play a game on my 360. I have a feeling it's bricked, but I have the original Orig.bin file I saved in my Documents during the first time I flashed my 360 months ago.