The type is defined in an assembly that is not ref

Question

I know the error message is common and there are plenty of questions on SO about this error, but no solutions have helped me so far, so I decided to ask the question. Difference to most of similar questions is me using App_Code directory.

Error message:

CS0012: The type 'Project.Rights.OperationsProvider' is defined in an
assembly that is not referenced. You must add a reference to assembly
'Project.Rights, version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

Source File:

c:\inetpub\wwwroot\Test\Website\App_Code\Company\Project\BusinessLogic\Manager.cs

Following suggestions here and here, I have deleted all instances of Project.Rights.dll inside C:\Windows\Microsoft.NET/*.* According to this, I checked if .cs files in question have build action set to "Compile". They do. I have also double checked that the .cs file containing the "Project.Rights.OperationsProvider" type is deployed to App_Code directory.

For some reason, application is not looking for the type in the App_Code directory. Since I've deleted all instances of Project.Rights.dll (that I know of), I don't know which assembly the error message is mentioning.

Answer 1

Maybe a library (DLL file) you are using requires another library. In my case, I referenced a library that contained a database entity model - but I forgot to reference the entity framework library.

Answer 2

When you get this error it isn't always obvious what is going on, but as the error says - you are missing a reference. Take the following line of code as an example:

MyObjectType a = new MyObjectType("parameter");

It looks simple enough and you probably have referenced "MyObjectType" correctly. But lets say one of the overloads for the "MyObjectType" constructor takes a type that you don't have referenced. For example there is an overload defined as:

public MyObjectType(TypeFromOtherAssembly parameter) {
    // ... normal constructor code ...
}

That is at least one case where you will get this error. So, look for this type of pattern where you have referenced the type but not all the types of the properties or method parameters that are possible for functions being called on that type.

Hopefully this at least gets you going in the right direction!

Answer 3

It didn't work for me when I've tried to add the reference from the .NET Assemblies tab. It worked, though, when I've added the reference with BROWSE to C:\Windows\Microsoft.NET\Framework\v4.0.30319

Answer 4

For me, this was caused by the project both directly and indirectly (through another dependency) referencing two different builds of Bouncy Castle that had different assembly names. One of the Bouncy Castle builds was the NuGet package, the other one was a debug build of the source downloaded from GitHub. Both were nominally version 1.8.1, but the project settings of the GitHub code set the assembly name to BouncyCastle whereas the NuGet package had the assembly name BouncyCastle.Crypto. Changing the project settings, thus aligning the assembly names, fixed the problem.

Answer 5

For me the reason why the error appeared was that the WebForm where the error was reported has been moved from another folder, but the name of its codefile class remained unchanged and didn't correspond to the actual path.

Initial state:
Original file path: /Folder1/Subfolder1/MyWebForm.aspx.cs
Original codefile class name: Folder1_Subfolder1_MyWebForm

After the file was moved:
File path: /Folder1/MyWebForm.aspx.cs
Codefile class name (unchanged, with the error shown): Folder1_Subfolder1_MyWebForm

The solution:
Rename your codefile class Folder1_Subfolder1_MyWebForm
to one corresponding with the new path: Folder1_MyWebForm

All at once - problem solved, no errors reporting..

Answer 6

Clean your solution and rebuild worked for me (in Visual Studio, these are options you get when you right click in your solution explorer), the error is gone in my project.