How did you enable the ajax?  I'm currently building a skin object that is using the accordian from the toolkit and did this:

Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
 'register AJAX
 AJAX.RegisterScriptManager()
End Sub

And all is working so far. 

For your case you may want to create a copy of the login.ascx and login.ascx.vb and move them to your own namespace so you're not changing the core files (otherwise you'll have to change them in every update).

Ryan

Sure thing... I tested this and it should work:

1. First create a directory in the DesktopModules for your new login skin object (or in the admin skins directory if you so choose, I do all of my development whether it be for Modules or Skin Object in the DesktopModules directories to keep things together).
2. Create a directory App_LocalResources in the directory you have the Login skin object saved. Copy the login.ascx.resx file from the Admin/Skin/App_LocalResrouces to the new App_LocalResources directory.
3. Open the login.ascx.vb file and change the namespace to your own, in my case I used YogIT.SkinObjects (the name of my company).
4. Open the login.ascx file and change the Inherits property to the new namespace (i.e. YogIT.SkinObjects.Login)
5. I had to make some minor changes to the code because the UI namespace was then duplicated. This could have been something from my work space, but just in case you see the same problem you may need to change the code: 
   
   Partial Class Login
   Inherits UI.Skins.SkinObjectBase
   
   To
   
   Partial Class Login
   Inherits DotNetNuke.UI.Skins.SkinObjectBase
   
   in the login.ascx.vb file.
6. Add the PreRender sub routine to the login.ascx.vb file:
   
   Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
   'register AJAX
   AJAX.RegisterScriptManager()
   End Sub
7. In to the top of your Skin ascx file add (if you are creating your skin in HTML edit the ascx file that is created after installing the skin):
   
   <%@ Register TagPrefix="yog" TagName="LOGIN" Src="~/DesktopModules/YogIT/SkinObjects/Login.ascx" %>
8. Then in the skin where you want the object to go enter:
   
   <yog:LOGIN id="yogLogin" runat="server" Text="Login" LogoffText="Logout" /> 

After you do all of that you should be able to add AJAX objects to your newly create SkinObject.

Good luck!

Ryan