RequiredEntryValidation triggers after clearing field

[Guest]

I have a FormView with a bunch of fields on it. One of those fields is used
to add a value to a DropDownList on the FormView by allowing the user to
enter a date and clicking a button. In the OnClick method I take the date out
of the TextBox and add its value to the DropDownList after which I clear the
TextBox value. When the browser redisplays the page the
RequiredEntryValidation error appears. The Date TextBox and the button have a
different ValidationGroup than the rest of the form.

Can I use this mechanism and not have the Validator fire under these
circumstances?

Any ideas on how to implement this would be appreciated.

Thanks!