What server are you attempting to connect to Dota APEM on? If you're trying to connect from USEast or Asia you will need to wait until the bot has had the chance to reconnect to those servers. APEM is currently offline for USEast while AREM is available to play.
There was a patch released today (1.28.5), and the bots were restarted from what I read. This can take some time for the bots to reconnect on some servers.
If you're wanting to play APEM i recommend connecting to one of the following servers: USWest/Europe/Eurobattle/ENT Connect (patch 1.27b only)
Most operating systems and DNS clients will automatically cache IP addresses and other DNS results, this is done in order to speed up subsequent requests to the same hostname. Sometimes bad results will be cached and therefore need to be cleared from the cache in order for you to communicate with the host correctly. All major operating systems allow you to force this process.
Hopefully that helps, and if you have any additional questions/issues please don't hesitate to ask.
Re: Cannot Join Dota APEM games, but could AREM Why?