This has been plaguing me since beta, as it has some others off and on. I think I finally found a solution. I tried running the game with all types of firewalls off and I didn't have the issue anymore. With all firewall settings off I let it run for a number of hours this afternoon while afk with no crashing to the login screen. After some experimenting this evening I think the culprit was my Comcast network gateway firewall in particular. When I lowered the security from medium to low this evening I did not get kicked for the hour and a half or so I played.

The difference between medium and low firewall settings for me is this:

Medium -

LAN-to-WAN: Allow all.
WAN-to-LAN: Block as per below and enable IDS.
IDENT (port 113)
ICMP request
Peer-to-peer apps:
kazaa - (TCP/UDP port 1214)
bittorrent - (TCP port 6881-6999)
gnutella- (TCP/UDP port 6346)
vuze - (TCP port 49152-65534)

Low -

LAN-to-WAN: Allow all.
WAN-to-LAN: Block as per below and enable IDS
IDENT (port 113)

While not a networking expert, does this mean the culprit is the "ICMP request" factor in the firewall settings?

At any rate, this worked for me and I hope it can work for some of you.