Got a Propellers rotating too fast error and ESC beeping after landing. Had it a few times. My mini has been stored in its case for a year.
The rear left motor was twitching after landing with this error, so I put new propellers on it.
The error continued, except this time, the rear right motor was twitching after landing, so I replaced the propellers on that one as well.
After that, the propeller overspeed error and ESC beeping have stopped and my mini is flying fine.
Threw away the old propellers as per the instructions.
I'm going to keep my Mini in the cupboard unfolded rather than risk bending more propellers having the drone in the case.
Thought I would share this.