Corel Draw X6 converts rectangle to curve.

I have a problem. I need a file containing a rectangle. I create it in CDR X6 and save it to X3 cause I have to open it on another computer that only has X3 available. But when i open said file in X3, the rectangle is aautomatically converted to curves. I need the rectangle to stay a rectangle to later use it as marks for my plotter. Is there any way to change that without drawing a "new" rectangle in a file opened in X3?