My process:
pour 2L of un-carbed beer from the fermeter or from the keg (uncarbed
beer in keg) into a 2L bottle and chill overnight. After chilling, I
leave 3 inches of headroom, squeeze out the air and bring bottle to
about 30PSI. I remove the CO2 line to avoide beer in the air line and
shake until I feel the pressure subside in the bottle and then re-juice
it to 30PSI. Again I shake, pressurize, shake, etc for about 20
minutes. I then bring to 40PSI and leave in fridge overnight.

This process yields a flat beer - what the heck am I doing wrong, the
instructions on the carb cap and other posts have made it seem so easy.

Thx,
Ryan