change date from "22-12-2012" to "12-22-2012"

Question

how to chnage date format from dd-MM-yy to MM-dd-yy in asp.net
 
I have date "22-12-2012" 
i want to change into "12-22-2012"
 
when i try to convert it gives me error
 
String was not recognized as a valid DateTime.