What does MissingManifestResourceException mean and how to fix it?

All I needed to do to fix this problem was to right-click the Resources.resx file in the Solution Explorer and click Run Custom Tool. This re-generates the auto-generated Resources.Designer.cs file.

If the .resx file was added to the project manually, the Custom Tool property of the file must be set to "ResXFileCodeGenerator".

The problem is due to a mismatch of namespaces, which occurs if you change the "default namespace" of the assembly in the project settings. (I changed it from (previously) "Servers" to (now) "RT.Servers".)

In the auto-generated code in Resources.Designer.cs, there is the following code:

internal static global::System.Resources.ResourceManager ResourceManager {
    get {
        if (object.ReferenceEquals(resourceMan, null)) {
            global::System.Resources.ResourceManager temp = new global::System.Resources.ResourceManager("Servers.Resources", typeof(Resources).Assembly);
            resourceMan = temp;
        }
        return resourceMan;
    }
}

The literal string "Servers.Resources" had to be changed to "RT.Servers.Resources". I did this manually, but running the custom tool would have equally well done it.

I just came across this problem today, and I found this Microsoft Help and Support page that actually did work around the problem.

I had a couple delegates at the top of my file, in the global namespace, and all of a sudden I was getting a MissingManifestResourceException when running the program, on this line:

this.Icon = ((System.Drawing.Icon)(resources.GetObject("$this.Icon")));

Then I moved the delegates into the namespace, got the same error. Finally I put the delegates in the only class in that file, and the error went away, but I didn't want the delegates in that class or namespace.

Then I came across that link above, which said

To resolve this problem, move all of the other class definitions so that they appear after the form's class definition.

I put the delegates (which I would not consider "class definitions") at the bottom of that file, outside of the local namespace, and the program didn't get the MissingManifestResourceException anymore. What an irritating error. But, that seems like a more robust solution than modifying the auto-generated code :)

I've run into a similar issue and, although I know it isn't the cause the OP had, I'll post it here so that if someone else runs across this problem in the future, an answer will be available.

If you add a class before the designer class you will get a MissingManifestResourceException exception at runtime (no compile time error or warning) because

Visual Studio requires that designers use the first class in the file.

For (slightly) more information see this post.