sys.ArgumentTypeException object of type 'object' cannot be converted to type 'Number'

This error comes when you are using ajax control on your page and also having some java script codes which include the built-in java script function with invalid arguments Or user defined function override the built-in function with invalid arguments.
e.g

function Number() {
var evnt = window.event;

if (parseInt(evnt.keyCode) >= 48 && parseInt(evnt.keyCode) <= 57) {
evnt.keyCode = evnt.keyCode;
return true;
}
else {
evnt.keyCode = 8;
return false;
}
}
Above function Number() is the actually built-in function with some arguments but here it is used as a user defined function width no argument.

Note: Change the function name or give the appropriate arguments to the function to resolved the above error.