What could cause Visual Studio / C# error MSB3105: Duplicate resources

Question

While working on an existing project I suddenly got the following error when trying to compile the solution:

error MSB3105: The item \"[filename]\" was specified

Answer 1

Be sure that under yourForm.cs no duplicate resources are defined (.resx). If you renamed your Form, remove the old resource because the new one during compile will be created with the new name.