The error has to do with the following code in default.aspx
<YAF:Forum runat="server" ID="forum" BoardID="1"></YAF:Forum>
and the error says:
The base class includes the field 'forum', but its type (YAF.Forum) is not compatible with the type of control (YAF.Forum).
I am sure it is an easy fix, but I haven't been able to track it down.