Subscribe by e-mail appears twice in plugins list then causes fatal error

I've uploaded the subscribe by e-mail plug in. When I do it appears twice on the plugins list. When I actiavte it, the Subscriptions menu appears in the WP menu column, however there is no settings option.

When I click on subscriptions I am transfered to the following page which returns the following message:

"Sorry, we can't find the content you're looking for at this URL. Please try selecting a menu item from above or to the side of this message to get where you'd like to go"

Attempting to navigate back to the plugins menu then produces this fatal error:

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 7680 bytes) in /home/sendings/public_html/wp-includes/kses.php(413) : runtime-created function on line 1

Deleting the sbscribe by e-mail plug in then restores WP to normal.