I have a dx9 renderer connected to a beamer that is running at 1024 x 768. I am mapping some objects, the beamer says that it is 1024 x 768 but the mapping is not correct and objects are a little stretched. Sometimes if fixes if i create a new renderer. Just then what fixed it was changing the background color!
thats a beamer problem not vvvv ! most beamer have some evil auto adjust mode, trying to cut off black borders. therefore if your background is black the projector looks for the next bright pixel and cuts off everything and the rest is stretched.
solution? well put some white quads in the corner of your renderwindow. or change background to color , go fullscreen and change it back to black.
good luck