ImageButton doesn't handle events in a UserControl?

[SyntaxError]

I'm unable to get a ImageButton placed in a custom user control to handle the OnCommand event.. but, when the exact same code is placed in the webform.. it works perfectly?

An example of what I'm trying to do:

<asp:imageButton imageUrl="~/images/sortLeft.gif" onCommand="sortBulletins" alternateText="sort ascending" commandArgument="memberEmail ASC" runat="server" ID="Imagebutton3" />

When the user clicks on the ImageButton, it postbacks to a procedure "sortBulletins" in the code behind:
Sub sortBulletins(ByVal sender As Object, ByVal e As CommandEventArgs)

'viewState("sortField") = e.CommandArgument

End Sub

Any help or ideas would be greatful!
Thanks,
Robbie