I downloaded the form and tried to replicate your error, even though I didn't really expect to know if I could answer your problem as Macropod was dealing with it anyway, I was interested in the problem, but I didn't get any issues, so I thought it might be something else like the version of windows (I'm sure I will be informed if not so - but that's how we all learn).

However, I would like to say I like the layout of your form, straight forward and easy to complete. Everything a good form should be so well done for that anyway. If you don't get many complaints from the "inputter" end then you know you have done a good job as we live in a complaining world.