This warning is shown when Men & Mice Central has lost its connection to Men & Mice update server. It is not mandatory to have this connection and it can be turned off. To fix this issue make sure that machine running the Men & Mice Update service and the machine running the Men & Mice Central are listening to the same TCP port.
TCP port 4603 is reserved for the update service but it can be changed if there is another software using that TCP port. Here is an article about changing the TCP port.