modal popup extender help

Hi I am having a problem with Modal Popup Extender control. I have two web user controls, sign in control and register control(I am not using the default controls provided by asp.net). On my start page if the user clicks on "Sign In" i want to show the sign in control in a popup. If the user clicks on "Register" i want to show the register control in a popup.

Now if i only have 1 modal popup extender(for sign in control), everything works fine as expected. But as soon as i add one more modal popup extender(for register control), both controls stop working.

Has anyone encountered a similar problem? Am i missing something?

Any help or tips will be great. Thank you for your time. -Sanjay.Maybe check for script errors during page load?