Could not find any resources appropriate for the specified culture or the neutral culture. Error not Resolved

I just hit this same exception in a WPF project. The issue occurred within an assembly that we recently moved to another namespace (ProblemAssembly.Support to ProblemAssembly.Controls). The exception was happening when trying to access resources from a second resource file that exists in the assembly.

Turns out the additional resource file did not properly move references from the old namespace name to the new namespace name.

In the designer.cs for the resource file, there is a static property to get the ResourceManager. Within that getter, the string was still referring the old namespace. Once correcting it to the new namespace, the problem was resolved:

global::System.Resources.ResourceManager temp = 
     new global::System.Resources.ResourceManager(
          "ProblemAssembly.Support.Properties.Stuff", typeof(Stuff).Assembly);

should have been:

global::System.Resources.ResourceManager temp = 
     new global::System.Resources.ResourceManager(
          "ProblemAssembly.Controls.Properties.Stuff", typeof(Stuff).Assembly);

Hope this helps the next person.

I realise this is an old question, however in case it helps anyone else searching here >>>

You need to set the .resx build action to "Embedded resource" for it to work with Data Annotations as in that example. When you add a .resx to an App_LocalResources folder the build action will be set to Content by default.

Also, in your example above, you added it to another project, so ensure that the Access Modifier is also set to "Public" (double click the .resx file to open the file and the Access Modifier is located along the top of the editor window).

Also ensure that you add a reference to the resources project from your main application.