Started seeing this recently. Client and Server are both 1.7.5. Server is local. Friends have no problems, just me. It happens consistently. I had hoped that bumping RAM and automating an hourly restart would make it less likely to happen. But, neither seem to help at all.
Most annoying when it happens at night. Your player can be left in the game and will be killed by hostiles if you are unable to log back in quick enough.
sigh. The problem seems worse with the 1.7.7 updated. Before, I was able to get around it by restarting the client and the sever. Now, it is much more difficult to get rid of. A few times, by restarting both client and server, then logging into a single player game, then back into the server helps. But, even then, it doesn't always come back.
Driving me nuts.