My computer is tripping can you tell me why?

okay i love making video's i have windows and i make my videos on window movie maker but every time im done publishing my video that i made i would exit off of window movie maker after then later on the day i would want to make another movie the when i press the link it would pop up >>> this sentence >>> another user is running windows movie maker on this computer plese close the other session of window movie maker befor starting movie maker again. and then i looked and i did and i have no idea what its talking about can you help me by teeling what to do without rstarting the computer or loging off