as quietman7 says, review the Malwarebytes 3 forum.
Two points - ensure that you are using the latest build of MWB3 - see the sticky post at the very top of the MWB 3 forum for the link to that. Note that this update may not be automatically presented to you immediately (or at all depending on settings). Download and run the update manually. You should be able to run the update 'over the top' of the previous version there is no need to unintstall the old version first.
Additionally (I don't quite follow which error you are describing), in earlier MWB3 builds there was some confusion as to whether MWB3 registered itself as the primary AV on the computer when Defender was the only other AV candidate present. The most recent MWB3 stable build (the one I referred to above) has an additional setting to give more control of that registration.
Edited by x64, 18 May 2017 - 01:38 PM.