Try adding the following to your form-property definition for Mcriteria:
Radio buttons don't submit a value if they're not checked. You therefore have to reset the value to null string so the required validation will recognize that nothing has been entered.
Also, just show the <html:errors /> tag once at the end and remove the property attribute. From what I understand, when you validate indexed properties, you only get one error message and it's a global one [ March 01, 2007: Message edited by: Merrill Higginson ]