I tested your form a bunch of times. It seems it will submit only if the name field has lower case letters only. If there are capitals it won't work. So check the validation rules on that field. Then try some test submissions with different combinations.
Next time someone tells you it doesn't work, contact them and see if you can duplicate what they did to make it fail. Get them to try all lowercase letters.
Unless you are losing money, it doesn't seem like it would be worth the time to invest in fixing this beyond doing the obvious. This may be fixed by the upgrade or just by redoing the form.
Before you do that look for the documentation on validation and be sure you are doing it correctly.
Here is what I would consider obvious.
1. Before updating, make a new form and see if it works better. If it does I'd still go ahead with updating the extension.
2. update the extension and check to see if the old form works.
3. Make a new form with the updated extension.
4. Contact
www.chronoengine.com and check their forums.
5. If that doesn't work. Get a different form extension that will work and has support.
Only you can decide if setting up a test site is worth it. If you're going to be losing subscriptions then there isn't any advantage in waiting for your new 2.5 site in my opinion.
If the operation of the form on the current site is critical, you'll need to get the chronoforms developers to help. They know their product best. It may be a bug they already fixed. If you can't work with them. Get another product with better support. You only have two forms, so it doesn't seem like a lot of work would be invloved, but they are critical to your income so getting something reliable and supportable is highly important.
See if it's a validation error.
Cheers,
Ed