The problem when builiding with Visual Studio and a Web Deployment Project:

Error 8 An error occurred when merging assemblies: ILMerge.Merge: 
ERROR!!: Duplicate type 'site' found in assembly 'App_Web_ilcyydph'. 
aspnet_merge 1 1 Website_deploy

 

This comes becauses some page classes have the same name...
Seach for the duplicate name in the whole site... and rename a class...

In my case, i added all Themes from the Mega Pack in my test blog,
some masterpages inherits classes with the same name:

<%

@ Master Language="C#" AutoEventWireup="true" CodeFile="site.master.cs" Inherits="site" %>

base class: public  partial class site : System.Web.UI.MasterPage

 

Renaming classes does the trick:

<%

@ Master Language="C#" AutoEventWireup="true" CodeFile="site.master.cs" Inherits="ZZZsite" %>

public  partial class ZZZsite : System.Web.UI.MasterPage

 

Et hop online Cool