I'm using a Web Application Project as a control library by wrting User Controls then using a Web Deployment Project to compile the .ascx files into an assembly and deploying that assembly along with the output of the Web Application Project to a Web Site Project that will use the controls. My Web Application Project builds, but my Web Deployment Project fails with the following error:

Error 108 Reference required to assembly 'Digop.EnterpriseControlRoom.CompiledUI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=05356650562eee27' containing the type 'Digop.EnterpriseControlRoom.ModuleControllerLayout'. Add one to your project.

Digop.EnterpriseControlRoom.CompiledUI is an assembly containing custom server controls that I'm using in my User Controls. The Web Application Project has a reference to this assembly. I can reference the controls in the code behind with no problem. I can create user controls in a Web Site Project that use the custom server controls in Digop.EnterpriseControlRoom.CompiledUI. Why can't  aspnet_compiler (used by the Web Deployment Project) find the assembly? The .vbproj project file has the reference in it. Do I have to declare the reference somewhere else as well (web.config?)?

I've noticed that in a Web Site Project, where the reference is found, user controls have CodeFile attribute and in the Web Application Project, where the reference is not found, they have a CodeBehind attribute. Does my problem have something to do with that?

Web application projects are really a hybrid of Web Sites and class library projects. The code behind files behave like a class library project in that they are built by VS on the client machine into an assembly that is pushed to the bin folder. The aspx page, on the other hand, is built at runtime by the asp.net build engine. The class which represents the aspx page inherites from the code behind class. In web sites, the code behind class is referred to by the Codefile attribute - this signals the asp.net build engine to build that class along with the class generated by the aspx page. This is the server side compilation model. WAP (and VS 2003 web projects) use the codebehind attribute, which is ignored by the asp.net build engine (which makes sense, since the code behind classes are built together by VS), however, the build engine does use the inherits attribute to identify the class to derive the page from.

To answer your question, the page, since it is built by the asp.net runtime requires a reference to the 'Digop.EnterpriseControlRoom" controls in order to build it. References for the asp.net runtime (which knows nothing about vbproj files) come from either the Bin folder, or from the <Assemblies> section of web.config (these are generally GAC assemblies). Normally, when you droip a control onto the webform designer, it will add the reference to web.config (if it is a GAC assembly) or add it to Bin (non-GAC assembly), for you. The following link has an example of how to add an entry to web.config.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpgenref/html/gngrfassemblies.asp.