User Control Parser Error: not a valid base class

[Guest]

I have an .ascx that gives this error:

"Parser Error Message: 'OurCompanyID.ThisAppNamespace.Menu' is not a valid
base class because it does not extend class 'System.Web.UI.Page'."

I didn't think it was supposed to extend 'System.Web.UI.Page'. This is the
start of the code in the .ascx.vb:

Imports System
Imports System.Web
Imports System.Web.UI.Page
Imports System.Web.UI.WebControls

Namespace OurCompanyID.ThisAppNamespace

Public Class Menu

Inherits System.Web.UI.UserControl

.....

We have a similar site on the same server that does not give this error.
What's more, if I run it from localhost, whether in or out of VS .NET 2K3, it
doesn't give this error. It's only when I run it from the server like the
end-user does that it gives the error.

I've tried re-building and copying the .dll to the bin folder; that doesn't
work. I've compared IIS properties for both sites. The biggest difference is
that the site that works is under the Default Web Site and the one that
doesn't is under a different web site. Nothing I've Googled has been helpful.

Any ideas?