Fatal error using Twitter Bootstrap 3.2.0

Updated to 1.7.2 and ran into this error:

Fatal error: Uncaught exception 'Exception' with message 'parse error: failed at&:extend(.clearfix all);/Applications/MAMP/htdocs/project-name/wp-content/themes/custom/bootstrap/less/mixins/grid.less on line 11' in /Applications/MAMP/htdocs/project-name/wp-content/plugins/wp-less/vendor/leafo/lessphp/lessc.inc.php:3460 Stack trace: #0 /Applications/MAMP/htdocs/project-name/wp-content/plugins/wp-less/vendor/leafo/lessphp/lessc.inc.php(2273): lessc_parser->throwError() #1 /Applications/MAMP/htdocs/project-name/wp-content/plugins/wp-less/vendor/leafo/lessphp/lessc.inc.php(121): lessc_parser->parse('// Grid system?...') #2 /Applications/MAMP/htdocs/project-name/wp-content/plugins/wp-less/vendor/leafo/lessphp/lessc.inc.php(753): lessc->tryImport(Array, Object(stdClass), Object(stdClass)) #3 /Applications/MAMP/htdocs/project-name/wp-content/plugins/wp-less/vendor/leafo/lessphp/lessc.inc.php(162): lessc->compileProp(Array, Object(stdClass), Object(stdClass)) #4 /Applications/MAMP/htdocs/project-name/wp-content/plugins/wp-less/vendor/le in /Applications/MAMP/htdocs/project-name/wp-content/plugins/wp-less/vendor/leafo/lessphp/lessc.inc.php on line 3460

If I commented out bootstrap.less, website loads but styling is no longer right since I’m using bootstrap’s mixins.

Advice to solutions would be very much appreciated. Thanks.

https://wordpress.org/plugins/wp-less/