Your problem could be caused by a number of factors. I suggest that you try the following:
1. When you cut the field and you draw the line that cuts it be sure that the line crosses the boundary of the field. The best way to draw the line for the cut is to start the line outside the field and end it outside the field (the parts of the line that are outside the boundaries will be clipped off for you).
2. There is a chance that the field that you are cutting is corrupted. Try deleting the field (along with the lines that make up the field) and then re-draw and define it then cut it.
3. If you continue to have problems send me an e-mail that has your address and phone number and we will send you the latest update to see if it might help.