To use a projection map, you need to render from the camera.
I will have at least two cameras in my scene. One is a still camera used for projection and the other is animated as needed for the shot. I will use the still (not animated) camera to make a render and then project the image onto the mesh.
If you use an orthographic view for the render then use a camera for the projection, it will not line up. Cameras do not create a perfectly flat image as they are curved due to the shape of the lenses. Orthographic views are completely flat. 3d cameras use a similar 'curvature' to their images and this will affect how the images look.
But I know how projection mapping works in generall... the problem here is that I cant textures the objects I renderer with an Othographic Camera view. Because the projection somehow seem not to align correctly!?