The units just can't be moved to any port outside of the French Atlantic coast. The error message mentions that some armies are locked in some theaters by scenario, so I tried detaching the non-II Army designated corps from the army, making them an independent stack, and moving them, but that is also not possible. I guess Parliament or the King or somebody doesn't want those guys outside of France. Seems odd, I'd expect that the player, acting in the capacity of the national high command, could decide to shift the emphasis from Northern Europe (where we have a constrained front because Belgium is still neutral) to some other part of the world.
"There is no substitute for victory"
Depends on how you define victory.