50mm 1.8 Err 001 at small aperture (f>=16)

Hi,

I'm new to the forum although I have read many posts here.

I have just received the 50mm 1.8 to use with my T3i which I bought 2 weeks ago. Whenever I set the f stop to 16 or larger (just to test the lens), I got Err 001 and had to re-attach the lens and set the f value down. The error appeared only when I pressed the shutter fully after the camera had achieved focus. I used AV mode. Is that normal and that I should avoid using such a small aperture or that my lens is defective?

Thanks a lot.