That is a very non-standard screen resolution. You might want to double-check the setting. The easy way to do that is right-click on the desktop, select Properties, and then the Settings tab. Your screen resolution will be shown in the lower left portion of that tab.
The only other cause that we know of, as bajantara mentioned, is resizing the window. It's very easy to accidentally resize the window while you're scrolling the map. The only way to fix that is to exit the game and launch it again. You can avoid that situation in VV:TLC by using the number keys to scroll around the map.
