In addition to copying UltimatePanel.dll to your bin folder, you should also add a reference to it in your project. Right-click References, select Add reference and point to the new dll under the bin folder of your web app.
Rather than copying aspx and vb pages from another app, add a new web form to your new app, and copy the contents of aspx and vb pages selectively. For instance, you shouldn't copy the Page directive line on top of the aspx page because it has its own Inherits property based on the namespace used in the other project. You can copy the remaining part. Similarly, you should copy the whole content of the vb page, but only the content of each method. If there is an event handler, you should generate that event handler method first in the new app, and copy the content of that method from the old one.