Unfortunately all poker clients will sometimes disconnect you or crash in various ways. Some more than other. The fastest attempt of a fix is to close the client and open it again. If thats not enough, it can sometimes help to restart your computer, before attempting to start the client again to get rid of whatever processes, that might be running in the background and disturb the poker client. If the problems happen on a regular basis over several sessions, then try to reinstall the client and/or change your internet provider, as already suggested.