There are many way to fix MsMpEng.exe error.
1. By adding MSMPENG.EXE to the Exclusion list.
2. Configure the task scheduler by changing the schedule defender scan.
3. Another easy but sure fix to msmpeng.exe antimalware service executable problem is to disable Windows Defender permanently.
4. Uninstall and Reinstall Microsoft Security Essentials.
Check out Techreviewpro.com for details.