Well, without seeing the lens and testing it on other cameras, best we can do is guess....
First thing I'd have ask is how you cleaned the contacts? I've seen it suggested to use a pencil eraser and I don't recommend that. Instead I suggest using a few drops of isopropyl alcohol to dampen a clean rag and carefully wiping the contacts on the rear of the lens with that (isopropyl alcohol or isopropynol is widely and cheaply available, sometimes is called "rubbing alcohol"). Keep off the lens optics. Also clean the contacts just inside the front of the camera, being careful not to touch the mirror or anything else. Those "pin" type contacts are spring loaded, too... gently press each one to make sure none are sticking.
If there is something on the electronic contacts interrupting the low volatage communication between camera and lens, it's often oils... finger oils, lubricating oils from the camera, etc. The problem with pencil erasers is that they are made from vegetable oil, so might not clear the problem. The mild alcohol will. Also particles of pencil eraser may get inside the camera where they could cause problems. (One reason pencil erasers are used on contacts is to remove oxidization... however, on all Canon cameras and lenses, the lens-to-camera contacts are gold plated precisely because gold doesn't oxidize).
About the only other thing you can do is try the lens on another camera and see if it does the same thing.
Since the error only occurs withint a certain range of focal lengths of the zoom, I think it most likely is a faulty or failing connection inside the lens. The camera is noting the lack of communication and suggesting cleaning the contacts, but that's not helping because it's something inside the lens causing problems.
I'm not familiar with that particular lens, but some (many?) have flexible electronic connecting cables, that have to move when the lens is zoomed or focused. If one of those wires fail or the connections at either end loosen, there's loss of communication.
It will probably only get worse. Look into having the lens repaired.
