date formatting

I am working on a form inserting the date.  I was hoping to add the day of the week with the date format.  I checked on the format and went to the custom selection and inserted dddd mm/dd/yyyy.  The hurdle I am trying to get past is, when I go to select a date, I receive a javascript error message telling me that it is the incorrect format that I should use dddd mm/dd/yyyy.  I am javascipt challenged, LOL.  Am I missing a setting somewhere or something? Any guidance or assistance would be appreciated.  I am thinking its a simple issue.

Thanks

Doug