Why is form not available?

We have a live form.  it has been working fine - and seems to be fine right now but yesterday it was not.  we got an error that said "this form is currently unavailable".  can you tell me why that would happen?  Our form is for audition registration and we really don't want someone to not register because the form isn't working.  

This form is currently unavailable message is usually displayed when the form is disabled or archived.

Your form is currently enabled (active). However, if you notice the issue again, get back to us so we will be able to check it.