My server spit out many of those Messages:
[09:38:54] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 10897ms behind, skipping 217 tick(s)

And after some time it Crashes with following Message:
[09:40:05] [Server Watchdog/FATAL]: A single server tick took 60,00 seconds (should be max 0,05)
[09:40:05] [Server Watchdog/FATAL]: Considering it to be crashed, server will forcibly shutdown.

I tried to give Java more Ram but even 8GB seem not enough.
Also I didn't found a suitable Issue report in the Tracker but this guy seem to have the same Problem.
http://www.minecraftforum.net/forums/support/server-support/2205991-1-8-server-crashing-skipping-ticks

best regards
HummingSwordsman