It seems, that MRT is causing serious trouble. The odd thing is, that I only use windows defender on my machines. I found the cause for mrt.exe error – it was caused by update kb 890830. Leon wrote within a 2nd that he had analyzed other updates (KB890830 and KB4014983) as a source of install conflicts, but at least he found the root cause. MRT obvioudly blocks installing other updates. Update KB4015550 is causing a MRT error 0xc0000005 (Access Violation) during install. I've translated the text, because it was written in a foreign language. I've installed update kb4015550 on another pc and received an mrt.exe – error 0xc0000005,

Last night I received also some e-mails from 'another source' (thanks Leon – but sometimes I have to take a nap ) reporting issues with update KBb4015550. I received yesterday some comments within my German blog, indicating trouble with update KB890830. On patch day (April 11, 2017) a new version of Malicious Removal Tool (MRT) has been released as update KB890830. Malicious Removal Tool (MRT) is shipped on each patch day to run once and clean systems from malware.

Microsoft kb890830