Canon Eos Rebel xti won't take a picture when zoomed in

When you change the zoom, chances are the camera lose focus, and you need to half-press the shutter button again to the camera autofocus.

Its normal behavior to lose focus when zooming in or out.

this does not seem to be like a problem in settings

please use a different lens and try the same

Clean the contacts on the lens? Your lens maybe defective need service?

Just a thought - are your Image Stabilizer and Auto Focus switches On or Off?
Might be worth experimenting with them.
Otherwise, sorry, can't help.
May be necessary to contact your vendor.

Zooming is done from the lens on a DSLR, assuming you have a zoom lens on the camera. For example, if your camera came with the 18-55mm lens, you should see the numbers 18, 24, 35 and 55 on the lens barrel with a white index line next to one of the numbers. Turn the barrel to move a different number next to the index line. 18mm is wide angle, 55mm is 'zoomed in'.

If u had took photo in very low light, pictures will appear blur. Or if you use tele zoom, u need to use tripod to stablize. In normal conditions, you can turn on image stablizer.

You can copy the photos to a temp directory, then have zoombrowser import the photos from that temp directory (instead of directly from the camera). This way you can utilize zoombrowser's naming function during the import.

Canon EOS Digital Rebel XT or XTi are both really really great cameras.

I think it might be a lens issue.
make sure you change the macro option. the macro must be activated if you are taking a picture of something which is close to the camera. if it's not activated, the picture will not be focused.
The same will happen if the item is far and the macro is ON.