Your server was killed by the watchdog. You can disable the watchdog, if you really just want a ‘make it work’ fix, but that’s a sign of a much deeper problem. The watchdog kills your server if a single server tick (which should take a twentieth of a second) takes a full minute. It looks like this happened during world saving, which is a pretty bad thing. That’s a sign of either a really obscure bug, a plugin listening to world-save and hanging, or you having an absolutely garbage storage drive coupled with a huge loaded area. My money’s on the latter, and if you’re running the sort of server that needs to load hundreds of megabytes of chunks, you cannot skimp on the server’s hardware.
Is there anything else you can give us that will provide more information? Things like plugin lists, full server logs, and a timings report would be great to start.