Error 500 on plugin update

Greetings!

When updating NinjaForms I get an error 500 on update:

“mod_fcgid: stderr: PHP Fatal error: Class ‘NF_Abstracts_Menu’ not found in /var/www/vhosts/proudlygmofree.com/httpdocs/wp-content/plugins/ninja-forms/includes/Admin/Menus/Forms.php on line 4, referer: http://proudlygmofree.com/wp-admin/index.php”

Any thoughts on why this might be occurring?

Thanks!

Sincerely,

//s// Jon C. Munson II