Generally, on a ToolStripButton, you can just set the Image on the property sheet, and the designer will automatically create the .resx file for your component and add it to the project (if you select local resource in the editor for the image). You can also select project resource from there, which will use the project's .resx file.You should never have to manually add an .resx file to a component... when you set a property that tries to use the resource file, it will create one automatically the first time it needs one.
Now, if it's giving you that error when you just try to set the Image property on a tool strip button, then there might be other problems...