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This doesn't help much, but...
I had no problem with my T2i.
Accidentally deleted after using ML by mistake during a format and re-installed no problem.
Review your steps. Maybe missed something.
Don't confuse, format vs firmware update, I did.

tried that, ive done it multiple times, still doesnt

Same here.  Using the latest firmware 1.0.9 and fully charged battery.  Doesn't work on two different SDHC cards (4 & 32 GB).  Throws error

On the 32GB class 10 I get:
Firmware update program
Update file error.  Please check the memory card and reload the battery and try again.

On the 4GB it just goes black and I get a blinking red light.

Afraid I'm going to fry my camera.  Just paid for v 2.3 and out of ideas.

the same thing happened to me that happened with your 4gb, have you been able to install it yet?

550d/t2i and i just tried the 2.3

I did everything the tutorial said to do, but my camera doesnt boot up with that "green screen", and i have been waiting for about 4minutes now even though the tutorial said it should take a quick second