I have a bit of a strange question, I am adapting the existing code base including the tile engine as per the book: XNA 4.0 Game Development by example by Kurt Jaegers, particularly the aspect that I am working on is the part about the 2D platformer in the last couple of chapters.

I am creating a platformer which has a scrolling screen (similar to an old school screen chase), I originally did not have any problems with this aspect as it is simply a case of updating the camera position on the X axis with game time, however I have since added a particle system to allow the players to fire weapons. This particle shot is updated via the world position, I have translated everything correctly in terms of the world position when the collisions are checked.

The crux of the problem is that the collisions only work once the screen is static, whilst the camera is moving to follow the player, the collisions are offset and are hitting blocks that are no longer there.

My collision for particles is as follows (There are two vertical and horizontal):

    protected override Vector2 horizontalCollisionTest(Vector2 moveAmount)
    {
        if (moveAmount.X == 0)
            return moveAmount;

        Rectangle afterMoveRect = CollisionRectangle;
        afterMoveRect.Offset((int)moveAmount.X, 0);
        Vector2 corner1, corner2;

        // new particle world alignment code. 
        afterMoveRect = Camera.ScreenToWorld(afterMoveRect);
        // end.

        if (moveAmount.X < 0)
        {
            corner1 = new Vector2(afterMoveRect.Left,
                                  afterMoveRect.Top + 1);
            corner2 = new Vector2(afterMoveRect.Left,
                                  afterMoveRect.Bottom - 1);
        }
        else
        {
            corner1 = new Vector2(afterMoveRect.Right,
                                  afterMoveRect.Top + 1);
            corner2 = new Vector2(afterMoveRect.Right,
                                  afterMoveRect.Bottom - 1);
        }

        Vector2 mapCell1 = TileMap.GetCellByPixel(corner1);
        Vector2 mapCell2 = TileMap.GetCellByPixel(corner2);

        if (!TileMap.CellIsPassable(mapCell1) ||
            !TileMap.CellIsPassable(mapCell2))
        {
            moveAmount.X = 0;
            velocity.X = 0;
        }

        return moveAmount;
    }

And the camera is pretty much the same as the one in the book... with this added (as an early test).

    public static void Update(GameTime gameTime)
    {
        position.X += 1;
    }