This paper investigates interference cancellation in an Uplink Multi-User (MU) Multiple Input Multiple Output (MIMO) system with imperfect Channel State Information (CSI), in which a Full Duplex (FD) Decode and Forward (DF) relay is used. Least Squares (LS) approach is considered to estimate the channels. In order to decode the symbols at the relay, the received MU interference is cancelled by applying Block Diagonalization (BD) based processors. Moreover, an equivalent relay is used to suppress the relay's self-interference signal. Afterwards, Minimum Mean Squared Error (MMSE) technique is adopted for the information extraction at the relay. A similar procedure is applied at the Base Station (BS) for MU interference cancellation and information extraction. Simulation results provide the appropriate number of users, antennas and pilot powers for each setup in order to achieve a relatively high sum rate.