IP and TP mediumtype issues

Hello,

I'm looking to solve an issue that has occured when I've chosen IP as mediumtype in the backbone when starting the project but want to change it to TP in order to get a linecoupler that is of an TP mediumtype. I've tried to change the areas mediumtype from IP to TP but I still get error displaying that the area is IP. How come it says it's IP even if I've already have changed it to TP in properties. Any solutions?