If your RootsMagic is running in Essential mode you will need to enter your key on the very first screen when you open the program. Sometimes you do that and it doesn't store the key. Then you need to right click on the RM icon on your desktop and select "Run as Administrator" and enter the key again. It should store it then.
If RootsMagic is already unlocked you will need to generate a wall chart the very first time, instead of opening a file previously created. Go to Reports>Charts>Wall charts and make a simple chart. It will store the RM Chart key properly and let you open the other charts now.