Form Calculation not working for all users.

We've set up a form for parents of students in our school to register for various programs.  Each program has a cost associated with it, and there is a form calculation widget on the forms that adds up the total cost of all the programs that have been selected.  (This total field is then used by the PayPal widget on the form to process payment.)

Some parents have reported that the PayPal widget does not show a total cost after they've selected a program, although it apparently works for the majority of parents using the form.  Do you know of any issues which would cause the form calculation widget not to calculate the total it's been set to calculate and then pass that value on to the PayPal widget?  Would, for example, asking people who experience this problem to clear their browser cache help?

Thank you.

I have also confirm that it works, the total is passed to Paypal:

In this case, do you happen to know in which browser version, or operating system they tried it? So we can try to reproduce the issue, and find the proper solution. In the meantime, I recommend you this:

1) Clear browsers cache

2) Ask them to load the form in Chrome or Firefox

3) Suggest them to make sure  JavaScript is enabled on their browsers: http://enable-javascript.com/