I have this same issue along with a few of my group members and it's with a map I created myself. I've tried uninstalling then re-installing the game, re-exported the map files and I even edited the map and altered a few things to see if any of the small changes to the weather, sky, portals and other few things would make a difference, but I still receive the "Cannot connect to map server" message :/ I had this issue starting yesterday and for the most part of the day I couldn't log into any custom maps other than one only though I can't log into it again right now.