Running a few experiments on the Empire side in the latest build, I think there may be a bug.  I can research to the armies tech, and build a war council in a city, and initially, I'll be able to build a group of units.  Over the course of a few turns, however, I lose that ability, as I design and try to build an upgraded unit group, the button for the group selection turns off.  When I try to go back to building the older troop type in a group, I no longer can do that, either.  Not very far into the game, so I don't think it's anything associated with that.  Resources aren't the issue, either; there's more than enough gold and materials for building the group.  I can post a debug if it will help, but I think in this case it's just a plain old bug, no crashes or slowdowns, so I don't know if that would help.

Winni