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

Hi there.  Just logged on and noticed your post, and since I also have the "nifty fifty" 50mm F/1.8 lens and a T3i, I thought I would check mine out.   I shot at F16 and then went down to F22, and both shots were 100 per cent OK.   I don't know what speed (ISO) you were using, but try it with a different ISO.   Other than that, I can't think of any reason you had the problem, unless your lens is defective in some way.   Was it new?   If so, it's guaranteed and you can take it back to the shop.   Also, google the error you got and find out what it means.  It's a new one on me.

Hope this helps.   Good luck.