Sorry for the long delay in answering, (I was trying to recover my password). I really don’t know HOW EXACTLY the problem was solved, the general instructions where right however. I used to the PPI to reset the MP panel to factory settings (I was asked to boot the MP panel). Then I once again reset the MP. It was then possible to log on to the control panel (the password was somehow reset). Thus I was able to enable the Ethernet channel in S7 transfer setting and perform an OS update.

I had the same problem with the MP277 panel and was struggling with trying to reset it to the factory settings. I tried with Windows 7, Windows XP, ProSave, WinCC Flexible 2005, 2008, TIA V12, V13, S7 PC USB adapter (6ES7 972-0CB20-0XA0), Ethernet, Transfer Mode on the panel...but nothing worked.

I finally managed to do it with the following configuration and  procedure:

I used

- Windows 7 PC with integrated RS232 port (COM1)

- Installation of TIA V13 Update 4 and WinCC Professional

- "RS232/PPI Multi-Master cable"  6ES7 901-3CB30-0XA0

I connected the panel and PC with the RS232/PPI Multi-Master cable and set the DIP switches to 1 1 0 0 0 0 0 0 (only DIP switch 1 and 2 were up, other switches 3-8 were down). The first three DIP switches are for setting the speed and  this set to 115.2 Kbps.

I turned on the panel.

I created a new project in TIA and added MP277 10'' Touch panel.

I opened the following menu: Online / HMI Device maintenance / Reset to factory settings.

I chose the following:

Type of the PG/PC interface: Com

PG/PC interface: COM

Select baud rate: 115200 and then clicked on Load.

I got the Establishing connection screen from Simatic ProSave V13.0.0.0 (OS Update) where I got the message "Please boot the HMI device"... I powered off and powered on the MP277 HMI panel and then the communication was finally established. I got "Read Information from HMI device" then "Clearing the Flash memory..." then "Downloading data..." 

The download started and reset to factory settings process completed in about 15 minutes and at the end  I got the fimessage "Please boot the HMI device..."

I closed this message,  I turned off and turned on the HMI panel and then the panel was reset to factory settings and ready.