Minecraft Server Crashing - SEVERE: Reached end of stream for /IP address

What actually happened was...:
The 1.5.2 Minecraft server was upgraded to 1.6.1 by downloading the 1.6.1 jar file and running it using "screen -dmS minecraft java -Xms1024M -Xmx1024M -jar minecraft_server.1.6.1.jar -o true". There are four to six players who have all upgraded to the 1.6.1 client. The old world under 1.5.2 was kept for 1.6.1.

They begin playing without any noticeable issue. Once the "SEVERE: Reached end of stream for /IP address" messages begin, block lag, normal lag, and delays with chunks appearing. Then the server crashed.