Hi, Im looking for advice on why my server keeps showing the error message "Incompatible FML modded server"

Whenever I try to join my server with forge installed (i'm on a mac btw) I see the error message " Internal Exception: java.netSocketException: Connection reset". I found out that on the right of the server theres a red "x", and when i hover over that it shows "Incompatible FML Modded server, server network message list is not compatible. Nobody but me has tried to join the server yet.