Not a very advanced user.
Have a spreadsheet designed to take a date and calculate
3 other dates (using the Workday function). I need help
accomplishing 2 things:

1st. There are 2 radio buttons. One of the 2 should be
selected before the date can be entered for calculation.
I am hoping that if a user goes right to enter the date
an error message will pop up reminding the user to select
one of the 2 radio buttons. I know this can be done with
Data Validation but I'm not sure how. Ideally when the
user enters data into the first date cell if a radio
button isn't selected, the message box will pop up, and
the formulas in the remaining cells will not execute.
How can I do this with data validation? If not with data
validation, then how?

2nd. Once the calculation is done I want the user to
press a command button that clears all of the text and
resets the 2 radio buttons to "unchecked". How do I get
the macro to set the radio buttons to "unchecked"?

Thanks for the help.