Disable RadDatePicker until another RadDatePicker receives input

[Raulis]

I have two RadDatePicker's. One holds a "date sent" value and another one a "date paid". The date sent value has to be before the date paid AND the date paid RadDatePicker has to be disabled until a date sent value has been set in a form. How would I achieve this? I thought a CompareValidator on the second control would prevent postback if the first input is empty but it seems that's not the case.

 

FYI I cannot use client side scripts on the same aspx page. I have a separate JavaScript folder that holds all my scripts and I cannot call $find("<%=RadDatePicker1.ClientID%>") . 

 

Help would be greatly appreciated. 

[Raulis]

Found a solution myself, don't worry about it.