Why am I getting an error message for the date when the date was selected from the date box?

I created a new form and the form started by giving an error message for a required field that was correctly filled out.  I changed the required option to not required and the form continued to the next page.  When it was time to submit the form the form gave an error message of "the date is not valid. The format is mm-dd-yyyy".  Which is the format the date is in when submitting the form.  Why is this error message coming up?  

I cannot seem to replicate this problem. But the error says the problem. It is likely because you have entered an incorrect date format. You should put 03-08-2018 instead of 3-8-2018. 

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