AP-5131 unknown input before marker

Refer to this awesome post about resetting your AP-5131.

I encountered the error "unknown input before marker" and could not find the answer.

In Putty, go to "Terminal" and then make sure "Implicit CR in every LF" and "Implicit LF in every CR" is checked. That resolved my issue.

Also, you must use a cable compatible with interfacing the AP and PC. I used a standard null modem cable - StarTech SCNM9FF2MBK .

Good luck!