I apologize for the late reply. Are you still experiencing this issue?
Not only Windows Defender, but also other antivirus solutions should be manually set to exclude your Arhcive folder. Can you make these modifications or disable your AV completely only a few minutes for testing purposes and then try again? Also, are there any files in ...Documents\MailStore Home\ ... with the ending .lock (MailStore.lock, MailStoreIndex.lock)? Then the database wasn't closed properly before. Can you manually remove those lock-files and try again?