I've experienced a few different issues trying to connect with other coins.  Sometimes I've seen issues with port mapping with UPnP.  You could try turning it on if it is off or off it is on.  I've run across other issues where I needed to turn off the router and reboot the computer.  Once I even had an issue with a config file where I removed all the old 'addnode' commands from it and put in a fresh list of nodes and things started to work.  Hopefully you can get things working.