use CauseValidation=false
on your button.
More discussion on the same are
- i must add CausesValidation="False" to every ASP Button to work, why?
- RequiredFieldValidator and preventing CausesValidation
Edit 1
Here is a similar question in stack overflow where on cancel button it does not validate
Form Validation With Bootstrap (jQuery)
Edit 2
I have edited the fiddle replacing the button with anchor for cancel then it work. So I think you can use link button for the same in your code.
Link for JSFiddle