Tried fixng 50mm 1.8 ef 11 t0 my canon20d and it kept on showing err 99,and soluti0n to fix it

The problem is that Err 99 is a very general, non specific error, so it could mean almost anything. The only time I had it was when trying to use older Sigma film lenses on my Canon 300d. I had to remove the battery to clear the error. It could be a lens problem that you have.