Similar crashes seem also to happen from time to time if (in case one of our guild's sectors is under attack and your guildmates just destroyed the siege) you try to replace a defending army and either the attacker is faster with setting a new siege or the sector is conquered by the attacker a split second earlier.
to reproduce:
1.) one of your guild's sectors is attacked
2.) your guildmates attack and destroy the siege
3.) you try to replace a defending army (or try to place one in an empty slot)
and then either:
4.) the attacker is faster by a split second (or exactly as fast as you?) and places a new siege
result: crash (internal error and auto-reload of the game) (frequency of the bug: I would say 3/10)
or
4.) the attacker is faster by a split second (or exactly as fast as you?) and kills the last defending army
result: crash (internal error and auto-reload of the game) (frequency: I would also say 3/10)
1.45.29432 (24.02.2015 1:15), Andi47 (73349), zz1, en_US, WIN 16,0,0,305, Windows 7, Firefox/36.0, 1920x917, DirectX9 (336 MB VRAM)