Error: appworks.materialSources is not a registered configuration

[Tony Gravagno]

I have AppWorks extensions enabled: React Style Helper, and React Generator. When loading a workspace with a React project, the Output Window shows this error:

[error] Unable to write to User Settings because appworks.materialSources is not a registered configuration.: Error: Unable to write to User Settings because appworks.materialSources is not a registered configuration.
at E.y (vscode-file://vscode-app/c:/Program%20Files/Microsoft%20VS%20Code/resources/app/out/vs/workbench/workbench.desktop.main.js:2297:54909)
...

This happens in the current VSCode v1.77.3.