It may be possible that MDMA is trying to access a secure slave. Make sure that the MDMA is configured as secure master. For example, the following C code can be used to configure the MDMA0 channels as secure master:
//Configure SPU to configure MDMA0 stream as secure master
*pREG_SPU0_SECUREP88=BITM_SPU_SECUREP_MSEC;
*pREG_SPU0_SECUREP89=BITM_SPU_SECUREP_MSEC;