In this letter, we develop a fully automatic robust linear receiver technique for joint space-time decoding and interference rejection in multi-access MIMO systems that use orthogonal space-time block codes and erroneous channel state information (CSI). The proposed receiver does not need any a priori knowledge of channel estimation errors and has a simple closed form. Numerical examples show that our method usually gives good performance in case of non-perfect CSI and/or low sample sizes when compared with other tested linear receivers.