Form submission stalls and never completes

Lately I've run into a BIG problem with form submissions.  It has happened on several occasions, but has reached unbearable levels now.  When someone completes the form and clicks Submit, the form never gives the Thank You screen.  Today, a person attempted to submit a form and the message said "I'm sorry but you can't submit two forms at the same time."  That's a new one.  Usually, the "Please Wait" message comes up and will remain there for hours if we let it.  The point is, in either case the submissions are never recorded nor do I receive them.  This is very important to my business and I can't tolerate these failures.  Please help!

Here is the form that received the "can't submit two" message.  https://secure.jotformpro.com/form/43386416869974

Jack

I cloned your form for testing purposes and was unable to reproduce the issue:

I then tested your form directly and was also unable to reproduce the issue.

Do you have your form embedded in a website? If so, could you please provide the URL so we can test?

We'll wait for your response.
Thank you.