Thank you! Had to downgrade Twig after running the updates to "2.6.2", but that got me up and going.

Following your lead, updated composer.lock file to 3.0.35 and it worked! Thanks!

Have a lot of work that I'd hate to lose. I'll send a request to Craft, thanks for trying to help and for the plugin!

Thanks, get C:\Users\rickn\Documents\Craft\Projects\Untye> composer require craftcms/craft Using version ^1.0 for craftcms/craft ./composer.json has been updated Loading composer repositories with package information Updating dependencies (including require-dev) Nothing to install or update Generating optimized autoload files Warning: Ambiguous class resolution, "modules\Module" was found in both "$baseDir . '/modules/Module.php" and "C:/Users/rickn/Documents/Craft/Projects/Untye/vendor/craftc‌​ms/craft/modules\Mod‌​ule.php", the first will be used. And no change to original error

Added in the composer.json code

Still getting the original error in the question However this time composer returned Warning: Ambiguous class resolution, "modules\Module" was found in both "$baseDir . '/modules/Module.php" and "C:/...vendor/craftcms/craft/modules\Module.php", the first will be used.

Replacing vendor/craftcms I then get yii\base\ErrorException: include(C:\...\Craft\Projects\Untye\vendor\composer/../craft‌​cms/redactor/src/Fie‌​ld.php): failed to open stream: No such file or directory in C:\...\Craft\Projects\Untye\vendor\composer\ClassLoader.phpy‌​ii