Lettace

So today I bought a level 50 from the pokeblock, and I am trying to add him to my team and seem to be un-able to do so. Please tell me how I could resolve this. I brought another pokemon this time level 66 I thought it was cause I used to be a low level now I know thats not the case, I have two level 100's and it seems to not be there. -Thanks Lettace