Canon today has posted firmware v1.0.5 for the EOS 20D.
The update, which comes on the heels of the ill-fated v1.0.4 earlier this week, incorporates a change in the firmware loader program that caused v1.0.4 to not install properly in some cases when a lens was attached, thereby rendering the camera inoperable.
In addition to fixing a bug in the firmware updater itself, v1.0.5 incorporates the fixes introduced in v1.0.4: the new firmware is designed to remedy situations in which the shutter button would no longer work, requiring the battery to be removed and reinserted before the camera would function properly again. It also makes unspecified improvements to the communication with CompactFlash cards.
Canon is suggesting that all EOS 20D owners, including those that have already loaded v1.0.4 successfully, update their cameras to v1.0.5. Doing so with no lens attached is among the recommendations on the firmware update page.
Owners of a 20D that is no longer functioning because v1.0.4 didn't install properly are asked to contact a Canon service centre.