DNS Pool isn't an error. It just means there is more than one server using that IP/DNS.
As far as not being able to connect, make sure Antivirus and Firewall software aren't blocking mIRC *OR* IRC and that your router isn't blocking IRC. Beyond that, check with your ISP to see if they block IRC ports.
You mentioned trying different servers, but try different networks as well. See if it's related to the network or not.