It sounds like one of the ribbon cables between the contacts at the back of the lens and the innards of the lens is either a little loose or has cracked preventing some needed communication between the lens and camera. At least part of the continuity problem may only occur when the lens is zoomed longer than 17mm. The entire reason for the ribbon cables inside the lens to begin with is to allow parts of the lens than move in relation to each other to communicate electronically. As you zoom out the continuity in at least part of one of the ribbon cables may become interrupted by that movement.

If the default aperture position is wide open aperture at 17mm then it appears the communication with the aperture when the lens is set at the 17mm position is enough to confirm the position of the aperture diaphragm. If you leave the Av set at f/2.8 then the camera doesn't need to communicate anything further to the diaphragm to take a picture. So even if you zoom the lens away from 17mm it works OK. But if you select a different aperture and then zoom, when the camera tries to tell the servo that controls the aperture diaphragm to stop down the instant before the photo is taken, it can't communicate with the servo and you get the error.

If you need a ribbon cable replaced it should normally fall under a "Standard labor service charge - out of warranty" repair at a Canon Service center. That first tier is the lowest charge for a particular piece of equipment. The price of the "Standard labor service charge" is based on the price of the item being repaired. Back a couple of years ago I had a standard repair done on a $2300 lens at a Canon service center here in the U.S. The "Standard Labor Charge" for that lens was $269 + $27 return shipping before my CPS (Canon Professional Services) discount. For the EF-S 17-55mm f/2.8 IS I would expect the Standard charge to be a bit less, since the list price of the lens was around $1,100 when introduced. With market conditions (primarily the stronger US Dollar vs. the Japanese Yen) the list price of that lens is now $879 in the U.S. and you can get a refurbished or good used one for around $600-700. So it would still probably only cost you about 1/3 to 1/2 the replacement cost to have the lens repaired. I'd guess around $180-200 for the repair and another $60-70 total for shipping both ways if you were in the U.S. In other countries YMMV.