For those shooting with the 450D, Canon has released a firmware update, version 1.0.9 which you can conveniently get here. According to Canon the fixes include:

• Fixes a phenomenon in which AEB (Auto Exposure Bracketing) shooting does not operate normally under specific conditions.
• Fixes a phenomenon in which the Live View exposure simulation warning indication does not properly display during Live View shooting.
• Fixes a phenomenon in which images cannot be played back after continuous shooting when a printer is connected to the camera or a video output terminal is used.

As always proceed with caution…