Error: Cannot find module 'uglifyjs-webpack-plugin'

This error message indicates that the module 'uglifyjs-webpack-plugin' is missing or not installed in your project.

To resolve this error, you can try the following steps:

1. Open your project's terminal and run the command `npm install uglifyjs-webpack-plugin`.

2. If the above command doesn't work, try deleting your project's `node_modules` folder and re-installing all dependencies by running the command `npm install`.

3. If you are still facing the same error, make sure that your project's `package.json` file has a dependency for `uglifyjs-webpack-plugin`. You can add it by running the command `npm install --save-dev uglifyjs-webpack-plugin`.

4. If none of the above steps work, you can try updating your webpack version to a newer version. Sometimes, older versions of webpack may not be compatible with certain packages.

Once you have installed the 'uglifyjs-webpack-plugin' module successfully, you should be able to run your project without any issues.