Firing modal popup with javascript

[rrocket]

I am trying to get a modal popup to display on an onblur event, but I keep getting a "'null' or is null or not an object" js error.

I have seen many examples using
[code=javascript]
var _popup;
_popup = $find('MPE');
_popup._show();
//And
$find('MPE')._s how();
//And
$object('MPE'). _show()
[/code]

But none of them work. I just need to fire the Modal Popup on the client side...

Code for the Modal Popup:
[code=c#]
<cc1:ModalPopup Extender ID="MPE" runat="server"
TargetControlID ="TestButton "
PopupControlID= "pnlWeightMessa ge"
BackgroundCssCl ass="modalBackg round"
DropShadow="tru e"
OkControlID="Ba cktoForm"
/>
[/code]

Thanks

[rrocket]

I figured it out.

Here is the info if anyone else has the same issue:
[code=html]
<cc1:ModalPopup Extender ID="MPE" runat="server"
TargetControlID ="TestButton "
PopupControlID= "pnlWeightMessa ge"
BackgroundCssCl ass="modalBackg round"
DropShadow="tru e"
OkControlID="Ba cktoForm"
BehaviorID="MPE " <!-- Added behavior to the control and named it the same as the ID-->
/>
[/code]
[code=javascript]
//Once I added the behavior this
$find('MPE').sh ow();
//worked to call the Modal Popup from the javascript function
[/code]