While trying to sync I got a "block checksum mismatch" in my debug.log file. Here is the last 30 lines. You can see that it happily downloading block, then it gets a network unreachable, then it has a fatal error:

2017-02-13 12:23:13 UpdateTip: new best=000000000000000005f83797c139814ac19f6df01ddb5a366ad0a8889eea9e4c  height=409620  log2_work=84.577937  tx=125928733  date=2016-04-30 20:50:36 progress=0.848096  cache=37.2MiB(19128tx)
2017-02-13 12:23:14 socket send error Socket operation on non-socket (88)
2017-02-13 12:23:14 connect() to [2a02:180:6:1::109]:8333 failed: Network is unreachable (101)
2017-02-13 12:23:19 UpdateTip: new best=0000000000000000020227bef01de871ccb17e3f6b9a86e9a2785001a71c6afe  height=409621  log2_work=84.577975  tx=125929755  date=2016-04-30 20:57:19 progress=0.848099  cache=64.3MiB(21625tx)
2017-02-13 12:23:23 Corruption: block checksum mismatch
2017-02-13 12:23:23 *** System error while flushing: Database corrupted
2017-02-13 12:23:23 Error: Error: A fatal internal error occurred, see debug.log for details
2017-02-13 12:23:23 ERROR: ProcessNewBlock: ActivateBestChain failed
2017-02-13 12:23:23 tor: Thread interrupt
2017-02-13 12:23:23 opencon thread interrupt
2017-02-13 12:23:23 addcon thread interrupt
2017-02-13 12:23:23 torcontrol thread exit
2017-02-13 12:23:23 scheduler thread interrupt
2017-02-13 12:23:23 net thread interrupt
2017-02-13 12:23:23 msghand thread interrupt
2017-02-13 12:23:23 Shutdown: In progress...
2017-02-13 12:23:23 StopNode()
2017-02-13 12:23:23 Corruption: block checksum mismatch
2017-02-13 12:23:23 *** System error while flushing: Database corrupted
2017-02-13 12:23:23 Error: Error: A fatal internal error occurred, see debug.log for details
2017-02-13 12:23:23 Shutdown: done

What is the problem?