You have to check and make sure you pulled him off the DL a few days ahead too. Otherwise the software throws a hissy fit. See if he is listed on the DL the next day or the next day after. Keep pulling him off the DL until he doesn't show up there on any day in the future say out to maybe 5 days.
Also, silly to ask Iknow, but you do have a roster spot cleared for him, right? If your roster is full you have to drop a player first before moving a person on the DL back on the roster. Again, silly to ask but sometimes we forget the basics when we are in a hurry.