All I can say is that it was working, then updates happened, and now I can't get it to work to play on the server I've been playing. Every time I try to get on the server, it says that it's outdated. I really don't want the Windows 10 version because I hear it's basically Pocket Edition. I downloaded 1.8.8, unzipped the files, and I forgot the following steps to making it all work. Could someone help me so I can play?
If you've upgraded to windows 10 and kept everything prior to update, (Apps and stuff) the original launcher and game should/will work.
COMPLETELY Ignore Windows 10 Minecraft as it's A HUGE down-grade.
If you've upgraded windows 10 on a clean install, you'll need to re-download the minecraft launcher from minecraft.net and select the version that you were previously running.
If you're trying to connect to a server and this message keeps occurring, you'll need to either down-grade the client, or upgrade the server. Prior to this, you'll need to know BOTH blient + Server versions.