Internal Server Error 500 when installing a plugin via WPMU DEV Dashboard

Trying to install the Google Analytics plugin via WPMU DEV dashboard, but it keeps throwing up this error:

Server error status: Internal Server Error [500]
https://www.dropbox.com/s/nm0s14i7mqykf3f/Screenshot%202017-02-19%2002.52.45.png?dl=0

Error logs give us this:

[Sun Feb 19 10:35:49.557935 2017] [:error] [pid 10312] [client 104.156.228.162:43039] PHP Fatal error: Class 'WP_Ajax_Upgrader_Skin' not found in /nas/content/live/cavityfreekids/wp-content/plugins/wpmudev-updates/includes/class-wpmudev-dashboard-upgrader.php on line 634, referer: http://cavityfreekids.org/wp-admin/admin.php?page=wpmudev-plugins

[Sun Feb 19 10:46:15.528910 2017] [:error] [pid 21742] [client 104.156.228.162:48227] PHP Fatal error: Class 'WP_Ajax_Upgrader_Skin' not found in /nas/content/live/cavityfreekids/wp-content/plugins/wpmudev-updates/includes/class-wpmudev-dashboard-upgrader.php on line 634, referer: http://cavityfreekids.org/wp-admin/admin.php?page=wpmudev-plugins

I uninstalled the main WPMU DEV dashboard and all other WPMU DEV plugins, reinstalled the dashboard, and am still getting the error.

Any thoughts?

p.s. hosted on WP Engine, they pointed me back to plugin developer.