Why cannot I move the camera by putting the mouse on the edge of the screen? Is this a bug or not? Help please!

That's just how the game is. You have to left click when the mouse is along the edges in order to scroll. You can also scroll with the arrow keys, if that's easier. You can also try out my Warcraft Mouse Helper utility, which maps the arrow keys to the WASD keys and the mouse scroll wheel to give you even more scrolling options.