Aluminum and fiberglass too
Originally Posted by BlackOmega
Are you sure it's plastic and not aluminum? Aluminum can feel a lot like plastic, and can be difficult to differentiate when painted.
I'm kind of doubting that it's plastic because of the force required to seat a cooler to the socket which is typically ~40lbs. of force. Plastic would distort too much.
However, an easy check to make sure that what I described is indeed your issue:
Set your rig back to stock clocks, remove the H50 and install the OEM cooler. If you no longer get the 55 code then you know it's bridging (shorting) a couple of circuits.
Give it a try.
PS: For what it's worth, with my boards I also updated the BIOSes and that made no difference whatsoever.