I am running Bitcoin Core 0.9.1. I had the blockchain up to date.

Suddenly the following message appears: "Catching up... Processed 296176 of 403423284 " and it stays like that forever. When I restart Bitcoin Core, everything works OK again.

It is the second time that this happens to me in the last 24 hours.

Relevant debug.log:
2014-04-16 17:29:14 ERROR: AcceptToMemoryPool : nonstandard transaction: dust
2014-04-16 17:29:25 ERROR: AcceptToMemoryPool : inputs already spent
2014-04-16 17:31:13 ERROR: AcceptToMemoryPool : nonstandard transaction: dust
2014-04-16 17:31:25 ERROR: AcceptToMemoryPool : inputs already spent
2014-04-16 17:34:16 receive version message: /getaddr.bitnodes.io:0.1/: version 70001, blocks=296175, us=88.0.116.192:8333, them=0.0.0.0:0, peer=88.198.62.174:9366
2014-04-16 17:35:13 receive version message: /getaddr.bitnodes.io:0.1/: version 70001, blocks=296175, us=88.0.116.192:8333, them=0.0.0.0:0, peer=88.198.62.174:17057
2014-04-16 17:35:15 socket recv error 10054
2014-04-16 17:36:40 UpdateTip: new best=000000000000000094e442bf42b8d557548c00419d58a501fc42c411e42005cd height=296176 log2_work=78.018546 tx=36974967 date=2014-04-16 17:35:59 progress=0.999998
2014-04-16 17:36:40 ProcessBlock: ACCEPTED
2014-04-16 17:37:57 receive version message: /Satoshi:0.8.5/: version 70001, blocks=1804588663, us=[::]:8333, them=[::]:8333, peer=5.104.224.42:34829
2014-04-16 17:37:57 Added time data, samples 40, offset +1 (+0 minutes)
2014-04-16 17:37:57 receive version message: /Satoshi:0.8.5/: version 70001, blocks=1596145119, us=[::]:8333, them=[::]:8333, peer=5.104.224.42:35534
2014-04-16 17:38:03 ERROR: CheckTransaction() : duplicate inputs
2014-04-16 17:38:03 ERROR: AcceptToMemoryPool: : CheckTransaction failed
2014-04-16 17:38:03 Misbehaving: 5.104.224.42:35534 (0 -> 100) BAN THRESHOLD EXCEEDED
2014-04-16 17:38:07 connection from 96.47.226.20:36702 dropped (banned)
2014-04-16 17:38:50 receive version message: /getaddr.bitnodes.io:0.1/: version 70001, blocks=296176, us=88.0.116.192:8333, them=0.0.0.0:0, peer=88.198.62.174:63699
2014-04-16 17:38:53 ERROR: CheckTransaction() : duplicate inputs
2014-04-16 17:38:53 ERROR: AcceptToMemoryPool: : CheckTransaction failed
2014-04-16 17:38:53 Misbehaving: 5.104.224.42:34829 (0 -> 100) BAN THRESHOLD EXCEEDED
2014-04-16 17:39:00 socket recv error 10054
2014-04-16 17:39:14 receive version message: /Satoshi:0.8.5/: version 70001, blocks=2018600785, us=[::]:8333, them=[::]:8333, peer=85.114.142.168:50558
2014-04-16 17:39:14 Added time data, samples 41, offset -12 (+0 minutes)
2014-04-16 17:39:14 nTimeOffset = +6 (+0 minutes)
2014-04-16 17:39:35 ERROR: CheckTransaction() : duplicate inputs
2014-04-16 17:39:35 ERROR: AcceptToMemoryPool: : CheckTransaction failed
2014-04-16 17:39:35 Misbehaving: 85.114.142.168:50558 (0 -> 100) BAN THRESHOLD EXCEEDED
2014-04-16 17:39:44 receive version message: /Satoshi:0.8.5/: version 70001, blocks=806550393, us=[::]:8333, them=[::]:8333, peer=109.163.234.13:62707
2014-04-16 17:39:44 Added time data, samples 42, offset -7 (+0 minutes)
2014-04-16 17:40:03 ERROR: AcceptToMemoryPool : nonstandard transaction: dust
2014-04-16 17:42:01 ERROR: AcceptToMemoryPool : nonstandard transaction: dust
2014-04-16 17:42:09 receive version message: /bitcoinseeder:0.01/: version 60000, blocks=230000, us=88.0.116.192:8333, them=0.0.0.0:0, peer=193.109.128.159:59739
2014-04-16 17:43:47 ResendWalletTransactions()
2014-04-16 17:44:01 ERROR: AcceptToMemoryPool : nonstandard transaction: dust
2014-04-16 17:44:46 receive version message: /Satoshi:0.8.6/: version 70001, blocks=296102, us=88.0.116.192:8333, them=37.157.220.12:8333, peer=37.157.220.12:8344