Popup Calender

I am trying to incorporate a pop up calender from Allen Browne. Downloaded
the file (for Access 2000 and later) from the address below and unzipped it.
http://allenbrowne.com/ser-51.html
I followed the instructions and also pasted the calendar button, changed
the name of the field to [VisitDate] in the onclick event as required. The
[VisitDate] is a date field and formatted for short date.

But when I click the button a type mismatch error occurs. The [VisitDate]
has some after update events already written. Is that the problem? Should I
paste the button first and then re-write the after update events?

Any help will be greatly appreciated.
Thanking you in advance
Leo