User210071364 posted
Rather late on a response, but I figure this might help anyone else coming along later...
- Make sure that whatever you're casting to (menu) includes the namespace.
- I used Page.Master.FindControl. Not sure that makes a difference, but worth a try.
- I'm developing in a Web Application instead of a Web Site. Might matter.
An example of what I used:
_includes.TopMenu menucontrol = (_includes.TopMenu)Page.Master.FindControl("TopMenu1");
Hope it helps.