If your XSi/450D has firmware update to Version 1.0.4, consider updating it to Version 1.0.9. The firmware fixes the following phenomenon:

• one in which Auto Exposure Bracketing (AEB) shooting does not operate normally under specific conditions.
• one in which the Live View exposure simulation warning indication does not properly display during Live View shooting.
• one 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.

When updating the firmware, be sure to carefully follow Canon’s instructions. They point out that a power failure during the firmware writing operation could disable the camera.

Canon advises that you use a fully charged battery pack or optional dedicated AC Adapter Kit for the update.

They also advise that you do NOT shut off the power, open the card slot cover or press any camera buttons during the firmware writing operation.

The update and full instructions can be downloaded at Canon’s website.