Here is a list of common build errors and their associated fixes.
Error loading plugins: plugin1, ...
This error happens because GitBook can't resolve a plugin (or the plugin is invalid).
External plugins need to be installed using gitbook install.
Need to install ebook-convert from Calibre
This error was logged as Convert of PDF - Need to install ebook-convert from Calibre #333 on GitHub.
To get around the error while trying to build your project as a PDF, ePub or mobi ebook, you must have the Calibre eBook reader/manager installed AND the command-line tools installed.
To install the Calibre command-line tools from the Mac version, from the menu select: calibre - Preferences - Miscellaneous - Install command line tools
Once this is completed, your ebook builds will be successful.