Zennoposter was working fine, but now I'm getting a Server not connected message... so no proxies are available because they're not being checked. What does this error mean exactly?
That means that you have problems with checkingprocessor.exe (try to add to exceptions for antivirus/firewall)
Or proxy checking script is unavailable (you can install your own on your server: http://zennolab.com/files/proxy.zip )
Make sure you use the latest ZennoPoster build (4.3.0.0)