As I've said before, I always taken extra steps to insure our systems are protected. I helped a friend about a month ago, which included installing Malwarebytes. During the process, I backed (created a ZIP file) of (Windows 8):
Well, my friend got the message "Malware Protection Enabled, Malicious Website Protection DISABLED" last night. Numerous reboots didn't help. He brought his computer over, I took the ZIP file, and unzipped the files into the original location (after a full scan with AVAST and Malwarebytes), rebooted, and all was fine. Then another scan (AVAST and Malwarebytes) was done, after Malwarebytes checked the updates to make sure they were current.
This is an idea to consider. I've seen a post here, and on other sites, with the same complaint. I know that this won't help a current problem, where a person hasn't backed up C:\Users\All Users\Malwarebytes\, but it will at least help you next time.
For people is the current problem. I suggest that you uninstall MB, make sure that the above folder is gone, then reinstall and try it again. If it works, then backup C:\Users\All Users\Malwarebytes\. On other OS's, it up to you to find the proper location.
Have a great day!