Not looked at your vcarve file as I don't have vcarve but if you are deleting a node & then redrawing a line it might be that the shape is not closed which will cause you problems. It will still look like a rectangle despite having 2 points that aren't joined together. Is there a close shape option in vcarve or if it has node editing functions the option to join & break apart nodes.
If you are having trouble importing the file then you could try saving in a different format, I believe vcarve will import quite a few vector formats so try exporting the design from scetch up as an EPS or PDF file.