MegunoLink

I have some problem in making it work with the Siemens IOT 20xx model in arduino mode .
For Example error response is this:

C:\Users\Gxxxxx\Documents\Arduino\libraries\MegunoLink\utility\Message.cpp: In member function 'void Message::LogTo(String&)':

C:\Users\Gxxxxx\Documents\Arduino\libraries\MegunoLink\utility\Message.cpp:89:33: error: 'class String' has no member named 'c_str'

Hi, we are not familar with that hardware. Did you have any luck?