TCP Multiplayer - Cannot load Savegame

Hello,

in TCP Multiplayer, I have a problem with the game crashing every few turns (seems to happen more often as game goes on)

After the Host pressed "Process Turn", it will work without error, however if we then select "Play Turn" we get a error message which says it cannot load the savegame-file (including path). This will happen on Host as well as on Client PCs independent.

I then need to fully quit the game to Desktop (I cannot load any savegames at all from main menu until done that), after which it will work perfecly fine ...
Until it happens again, which can be as often as every 2nd turn.

Host is Windows XP Pro. SP2 with a Intel CPU, 1GB RAM, 3GB Pagefile, Clients are WinXP Pro SP2 as well, some Intel, some AMD CPUs, Nvidia and ATI Gfx-Cards.
Host has newest ATI drivers for a R9800, Clints both have Nvidia with newest drivers, not sure which card it is, but they are kinda new.

Network is over a 1Gbit Switch (D-Link) with some cheap Network Cards (8169 Realtek-Chipsets), Host has a D-LINK DGE-530T

All in all we dont have much problems anywhere else.

Windows XP Firewalls are deactivated while we play.

hope someone has a Idea, as it makes playing TCP over Internet Imposible (esp with the Problem about Host having to end his Turn first)