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Any link to the form?

Yes, sure here https://goo.gl/4jNywO

This should be the same error as in https://www.ads-software.com/support/topic/php-catchable-fatal-error-v-1411

On submitting the form you hit a 500 error. I can see that you have that W3 Total Cache installed. That leads me to that conclusion.

As you are the 2nd user of this cache plugin that files a bug, I will release a bugfix this evening.

Thank you so much! it works perfectly! great plugin and great work!