VPN goes down at random

I have a strange problem with SG210, the VPN site-to-site to Cisco ASA 5520 dies a couple of times a day. 

I've attached the log, the messages that are in the end of the log continue until the VPN connection disabled and re-enabled, at which point VPN is up again for some time.


2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13352: DPD: Could not find newest phase 1 state
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13352: DPD: No response from peer - declaring peer dead
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13352: DPD: Restarting all connections of peer
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13352: DPD: Terminating all SAs using this connection
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13353: deleting state (STATE_QUICK_I2)
2015:06:08-21:56:49 bog1fwcl-2 pluto[10598]: id="2204" severity="info" sys="SecureNet" sub="vpn" event="Site-to-site VPN down" variant="ipsec" connection="REF_IpsSitVpnTST" address="x.x.72.70" local_net="x.x.74.2/32" remote_net="x.x.200.6/32"
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: id="2204" severity="info" sys="SecureNet" sub="vpn" event="Site-to-site VPN down" variant="ipsec" connection="REF_IpsSitVpnTST" address="x.x.72.70" local_net="x.x.74.2/32" remote_net="x.x.200.6/32"
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13352: DPD: Restarting connection "S_REF_IpsSitVpnTST_0"
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13352: DPD: Terminating all SAs using this connection
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13352: deleting state (STATE_QUICK_I2)
2015:06:08-21:56:49 bog1fwcl-2 pluto[10598]: id="2204" severity="info" sys="SecureNet" sub="vpn" event="Site-to-site VPN down" variant="ipsec" connection="REF_IpsSitVpnTST" address="x.x.72.70" local_net="x.x.74.2/32" remote_net="x.x.220.21/32"
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: id="2204" severity="info" sys="SecureNet" sub="vpn" event="Site-to-site VPN down" variant="ipsec" connection="REF_IpsSitVpnTST" address="x.x.72.70" local_net="x.x.74.2/32" remote_net="x.x.220.21/32"
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: DPD: Restarting connection "S_REF_IpsSitVpnTST_1"
[DPD Restarts the VPN]

2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: initiating Main Mode
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: ignoring Vendor ID payload [FRAGMENTATION c0000000]
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: ignoring Vendor ID payload [Cisco-Unity]
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: received Vendor ID payload [XAUTH]
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: ignoring Vendor ID payload [c6d54f8ae3717cb429ebe770e86ddad8]
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: ignoring Vendor ID payload [Cisco VPN 3000 Series]
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: received Vendor ID payload [Dead Peer Detection]
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: Peer ID is ID_IPV4_ADDR: 'x.x.201.30'
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13365: ISAKMP SA established
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13366: initiating Quick Mode PSK+ENCRYPT+TUNNEL+UP {using isakmp#13365}
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_0" #13367: initiating Quick Mode PSK+ENCRYPT+TUNNEL+UP {using isakmp#13365}
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13366: ignoring informational payload, type IPSEC_RESPONDER_LIFETIME
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: id="2203" severity="info" sys="SecureNet" sub="vpn" event="Site-to-site VPN up" variant="ipsec" connection="REF_IpsSitVpnTST" address="x.x.72.70" local_net="x.x.74.2/32" remote_net="x.x.220.21/32"
2015:06:08-21:56:49 bog1fwcl-1 pluto[11676]: "S_REF_IpsSitVpnTST_1" #13366: sent QI2, IPsec SA established {ESP=>0x80f44d2c 0x72fd0ac5 

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