Hey guys, I was having a similar issue and resolved it. Here's the article I used and I'll give little explanation into my issues. https://support.apple.com/en-us/HT201295 The password I use to log into my device wasn't working for the system preferences lock. I tried resetting my password via the activation lock but received the same message you did. Resetting the SMC chip may solve the issue some of you are experiencing - it at least worked for me