Gantry has a mind of its own!

[kimdoc103]

Hi everyone, we are having a problem with our Heath shape cutter gantry. We are running on a Burney 5 and programming using pro-nest. For instance, I programmed a 4x8 sheet this morning with rectangles nested on top of each other. The first one cut fine and then when it went on to cut the next, the pierce started at least an inch over from where it should have been. I reprogrammed and it still did the same thing. Any idea on what could be the cause???