Fatal error on homepage after installing this plugin

Hello!!

I liked your plugin. It solved my problem of a customized login page but created another problem.
I am using the wordpress theme “Marketica”. I contacted the theme developer but they asked me to contact the plugin developer.
After I installed the plugin, the revolution slider, visual composer and a few features of my website are not working properly. Including my website homepage is displaying
“Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 340851 bytes) in /home/monika191/public_html/wp-includes/shortcodes.php on line 223”
I want to use your plugin but why am I getting these errors?
Please help.

Regards,
Monika