Generic failure, like parsing or an invalid integrity check. Fallback for anything else as well.
Everything ok.
Server is sending wrong information about its own IP address (unrelated to player count spoofing)
Any sort of timeout after the server acknowledged at least one packet. Eg. a2s rules times out after info worked
Either A2S rules is unsupported, or the Server has not been updated to any 1.* version eg. pirated servers
No connection can be established as server actively refuses it.