There are two ways I know of to get something like this:
1. You've detached all the units from the subordinate commanders. You can check this in 3D view by moving the mouse over each corps commander in turn to see if he has any units under him.
2. You have run out of aides de camp to carry orders. Look at the CinC's unit info card at the bottom. There will be a quill pen icon and the number of available aides de camp underneath it. If it's zero, you'll have to wait until one or more return. This might happen with a small OoB.
If neither of these situations is the case, send the file to JMM with an explanation of what the problem is so he can look at it for possible bugs. JMM@histwar.com
Hook