This error occurs because some resources could not be loaded from the resx file. If the .resx file is not associated with the Picture class file in the project, the resources cannot be loaded. Use the "+" mark in the project treeview to view the .resx file associated with your Picture. Here is a screenshot of a "bad" resx file association. Notice the icon is blank:

Here is a screenshot of a "good" resx file association:

To fix the problem: right click on the .resx file and select "include in project".
If you wish to fix your project in a text editor, close your project. Open the .csproj file using the File/Open File menu command. When you open it, select "Open With..." and select the XML editor. Now you can edit your project file directly. Skip down to the ItemGroup section containing EmbeddedResource tags. Add a new EmbeddedResource tag for your bad Picture class:
