I am trying to configure my MVPx10 gateway, but I can't save the configuration info as the default configuration and boot via the RS232 configuration software. How can I enable write access?

The reason you are getting read only access is because someone either logged into the VOIP before you over the Web browser or you didn't log out properly (choose 'logout' from the config pane before closing the session). Please close the software, disconnect the ethernet cable and power cycle the VOIP. Doing this will disconnect any current connection and reset the VOIP so you can have read / write access via the COM port.