error: The TargetControlID of is not valid. A control with ID txtDate could not be found.

Try declaring the control in the page.

I encountered a very similar error. In my case, the page that dynamically created the controls and extender used a master page. When the master page was removed, the code worked.

Here's my post:http://forums.asp.net/thread/1674298.aspx

Can anyone explain why or how to solve this general problem? It's silly to say "If it doesn't work, then don't do that."

Hi,

I "hope" i′m too late to give the answer ;-)

you can do this also without designer. For instance if you are build webparts you have to code.

You just have to set theID property of your Textbox control to"txtDate"