I’ve just discovered this firmware upgrade for the 5D Mark II which includes the following two improvements/ fixes:

  1. Supports the WFT-E4 II wireless file transmitter that was released in December 2009.
  2. Corrects a phenomenon in which visible noise may appear in images taken by continuous Bulb shooting.

For full details and to download the update goto:

http://web.canon.jp/imaging/eosd/firm-e/eos5dmk2/firmware.html

For an up-to-date release history of Canon Firmware versions goto:

http://web.canon.jp/imaging/eosd-e.html