Plugin could not be activated because it triggered a fatal error.

This is a very old issue, maybe a year, yet remains unaddressed by the plugin author/maintainer.

See the thread “Badly broken ( fatal error ) with any PHP after PHP 5.0.x ( function removed )” in this forum, but also start your search and migration to something else.

This problem is fixable please see the following post from the support forums.

https://wpmingle.com/forum/mingle-plugin-forums-group2/support-forum1/plugin-fatal-error-thread2133.0/#postid-7246

The plugin itself is not all that great but may solve some problems for people.