Fatal Error: Allowed memory size exhausted...

When I deactivated a few wordpress plugins, I got this error. Some of them were WPMU plugins like Membership2, I also deactivated other plugin like Coming Soon by Seedprod, so I'm not sure which ones are causing this, or if it's caused by something else all together...

ERROR MESSAGE:

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 49152 bytes) in .../public_html/wp-admin/menu.php on line 97

Sometimes I get this error messages too when I hit refresh.

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 12288 bytes) in /public_html/wp-content/plugins/wp-defender/app/class-wd-post-model.php on line 216

The error message comes up every time I try to go to my dashboard... I'm not proficient in programming of any language, so I'm not sure how to solve this... Do I need to delete everything and do a fresh installation of Wordpress? I would really hope not to...

For reference, here is the website I am working on:
http://www.cpetaxacademy.com