将Ajax Calendar控件创建的文本框值传递给变量时，String未被识别为有效的DateTime

I'm trying to pass the date value populated into a textbox by an Ajax calendar extender control to a date variable but I keep getting a 'String was not recognized as a valid DateTime' error. I've tried modifying the specific date format when populating the variable but keep getting the same error. Can anyone tell me where I'm going wrong?I'm trying to pass the date value populated int