Troops are never in place on the front line. Help!!!

When I put my troops in a front line I wait for them to organise themselves until it stops saying "-50% some troops are not in position" in the army bar, but, as soon as I click the button to tell them to put the plan into action it starts saying that they aren't in position anymore and gives me a 50% reduction. It's very frustrating and screws my whole game up. If someone knows how to fix this problem or if it's just me being an idiot please help.