Use the line by line debugging to tell where exactly it crashes... Basically one of your 'enemymovement' object isn't defined... Also... I suggest you look into the System.Drawing and System.Image I think... Using pictureboxes is a very bad way to do what you're trying to do Basically, load the images in some Image objects, then just paint them wherever you need on your window, which could be a picturebox, or you can draw directly on the form I think. You should also use structures for your enemies, instead of the tag thing. The structure could hold various information, such as the current location of the enemy, its remaining energy, if it's dead or not, etc.