Hi isteve,
The date pickers ship with five Validator controls.
1. Compare Validator
2. Difference Validator
3. IsDate Validator
4. Range Validator
5. Required Field Validator
The Microsoft Validation controls will not work with the date pickers. This is because the Microsoft Validators do not deal properly with DateTime objects server-side. Since the date pickers pass around DateTime objects exclusively, we had to extend the Microsoft Validators for this requirement.
If you have not already done so, we would highly recommend upgrading to the v1.2 release of the controls. You can find download information at the following location. See http://forums.basicdatepicker.com/forums/505/ShowPost.aspx
If you are using the full version date picker (BasicDatePicker) you might want to investigate the OnClientAfterSelectionChanged Event that fires client-side when the date is changed.
Hope this helps.
Thanks,
Geoffrey McGill
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Coolite Inc.
Email: support [at] coolite [dot] com
Phone: +1(888)775-5888