After submitting the form, the server returns an error indicating null field provided there is no proper error handling techniques employed on the server side script.
Date being selected by the user is in DD/MM/YYYY format.
Set the Value To Compare server-side to the current date.
What's up with that requirement that "validation should not be done by using ASP controls"? They are designed specifically for these kind of scenarios. NET model then I try to stick with that model even to the extent of inserting client-side code using the Client Script Manager instead of directly including Java Script.