First off, im sorry for posting this, I know the question has been up a lot of times but none of the answers I found seem to solve my problem.

I have a modalpopup on a page and inside the modal's popup box I have a custom usercontrol. This usercontrol is a login form that either validates and sends the user to another page or fails and returns an error.

Now I found 2 solutions for this, ill post them and the reason I can't use them.

1. Put an updatepanel inside the modal's popup window.
This would solve the problem that the modalpopup dissapears after postback (when a wrong username is entered). However I run into a problem, it seems like Response.Redirect isn't working when doing a postback form inside an update panel.
2. Modalpopupcontrol.Open() (Or something like that) in code-behind
This would make the whole-page-postback a lot less painful but my problem is I can't access the ModalPopupExtender from inside the Custom User Control.

I have tried something along the lines of
 

Page.RegisterStartupScript("reopenPopup",<script type=\"text/javascript\">$find('ctl00_ctrl00_mdlPopup').show()</script>")

Rather than doing a postback from your login control why not asynchronously call a Web Service or a PageMethod. Then depending on the result you can choose to redirect the page via javascript or handle the error.

 http://msdn.microsoft.com/en-ca/library/bb398785.aspx

Dakani,

With regard to #1, instead of using a Respose.Redirect (which, as you say, doesn't work with partial postbacks), which why not try doing a ScriptManager.RegisterStartupScript() to inject some javascript to redirect your page: window.location = "http://some_address"

James