Combining units

[Flop]

Does anyone know why some generals can only make brigades with 1 unit? I'm specifically thinking of Katte and Normann, at the beginning of the grand campaign. I'm trying to make a brigade of cuirassiers, but if I try adding more than one unit of cuirassiers, the button greys out. Other leaders are able to do so, and in fact, the cuirassiers are from Gesslers brigade, so they're already in a brigade. What am I missing?

[Ebbingford]

The leader must be active when you select the "Form brigade" button and not in a stack with any locked units.
You need to select this button to form brigades, if you don't all you can do when you press the "+" button is embed the leader in the unit, like Norman is originally.

[Flop]

Thanks. I realized that I hadn't enabled brigade command for those commanders. I wasn't aware that you could still embed them in a unit, though.