The manual doesn't mention maximums for the number of units in a scenario. I've run into freezing the game when creating a huge battle with 2 reinforced battalions per side. Anybody have more information? When I say two reinforced battalions, I am talking about the reinforcements being elements of the same battalions, arriving later.
I begin with a company and over 7 reinforcements I introduce the rest of that battalion and several more companies from two others. There are also a platoon of tanks or destroyers, some artillery, and perhaps an air unit per side. To get through the battle, I've had to remove all jeeps, trucks, and other vehicles that are not armed. I have deleted the supply units. I also save every turn so that I can continue when restarted.
My computer has 8 Gigs of RAM and a Nvidia 7xx video card with 2 G memory. It is strong enough. I think the issue is in the programming, as the game sets up a set amount of memory to work with - within the Windows OS.