ASP.NET web controls

I'm getting the following error: ...................... Multiple controls with the same ID '_1' were found. FindControl requires that controls have unique IDs. ..................... I get this on a postback of a page with user control which has some custom controls on it. ...

I have a User Control that renders all asp buttons as Command button vs. Submit buttons.  When you view source on the browser you see the HTML rendered: <input type="button" ... > instead of <input type="submit" ...> ...