I also had issue with H77TN and Crucial M4 120GB mSATA drive. In my case when mSATA was inplace it messed up readings such as temperatures, they always showed 255 C in bios and it lost fan speed control, it was on full speed.
Otherwise the OS booted and HDMI/other ports worked.
Gigabyte was not much help, only sent me a short list of supported mSata drives, largest drive was 64GB i think.
The same mSATA works fine in another full size Gigabyte board.