why does form submission come up as a 404 error code?

A student tried to submit an application through one of my jotform forms, and they kept receiving the 404 error code. The submission went through, but the student did not know. 

I have checked your above indicated form, the issue is that the Thank You page you have selected that After submission redirect to a Custom URL, which is http://pmch.utmb.edu/phtrack, this url is the one that has not acces, rendering the 404 error code.

Please look at the following figure:

In order to fix this you can go ahead and select a normal Thank you page, while the URL is fixed.

Let us know if we can assist you further.