I'm creating a form to search for records via TextBoxes for Name, Number, and Date. If all boxes are empty, I want the DataSource to return 0 records. When the form loads, all the text boxes are empty, and I get error:
Conversion from string "" to type 'Date' is not valid.

That is probably because you are calling your code on Page_Load; move the code to a seperate method and have a button click or something call your code. Also, this is a bug. You need to test for the absence of data else your script will bomb everytime someone tries to search and they leave the date field blank.

if(this.txt.Text == String.Empty)
{
  //do something
}

Alternatively you can do

if(this.txt.Text == "")
{
   //do something
}

================================================== =========
Read this if you want to know how to get a correct reply for your question:
http://www.catb.org/~esr/faqs/smart-questions.html
================================================== =========
Technical Editor for: Professional Search Engine Optimization with ASP.NET
http://www.wiley.com/WileyCDA/WileyT...470131470.html
================================================== =========
Why can't Programmers, program??
http://www.codinghorror.com/blog/archives/000781.html
================================================== =========

You could also use the method "String.IsNullOrEmpty(value)" to check. It will return true if there is null or empty or return false if it isn't. This works good if you have a null as I believe the other way throws an exception if there is a null. I play with nulls a lot. :)