You haven't unlocked your bootloader.
The flashing Red LED is the notification that a locked bootloader has encountered a ROM that is not based on Sony's releases. (CM, AOSPA, AOKP and so on.)
You need to unlock your bootloader to flash any ROM found in the Original Android Development section, and in the other Dev section only those marked LB can be installed with a locked bootloader.
NOTE: Doing so will erase the TA partition (which holds the DRM keys which allow X-Reality, Gracenote and other things to work.) and WILL NOT BE RECOVERABLE
unless you back it up.
To back up the TA partition you will need to be rooted on a stock ROM.
Read the following thread, then read it again three more times before proceeding any further.
And if you bought your Phone from Bell Canada, they won't let you unlock your bootloader.