Yesterday I got a Crucial M500 240GB SSD with firmware revision MU03.
I downloaded Crucial® Storage Executive. After running the web ui, it prompted me to update the firmware version from MU03 to MU05. I confirmed the action and after rebooting some error message was shown before booting into Windows. I tried several times, but it failed every time.
Then I looked into the issue carefully. The update utility creates a temporary bootable device labeled "Micron" and the device couldn't boot due to some file missing. The error message shown was something like this (I don't remember it exactly).
> Micron SSD Update Utility > initrd /core.gz > /core.gz not found
Then I rebooted my PC, entered into BIOS settings (for me it's Del button), turned on UEFI Boot for Storage and Optical drives and restarted the update process.
It took 3-4 minutes. The update operation was successful.