scurvy dog

I am new at the game. I started the 1939 campaign as axis and found I could not reinforce my units with elite reinforcements. The elite reinforements option was grayed out on the drop down menu that comes up when you right click a unit. Regular reinforcements and all other options were available. I know you can't get elite reinforcements for units that are adjacent to enemy units. Are there any other restrictions that I don't know about? Am I doing something wrong? Please help.