[SOLVED] Front end users plugin generates "Fatal error: Allowed memory size xx bytes

Hello all and thank you very much to the producer(s) of this wonderful theme, Montezuma.
I've tweaked it very little, since I'm no expert in anything here, really.
What I noticed is that "Front End Users" plugin (http://wordpress.org/extend/plugins/front-end-users/)
seems not to work, even with default settings. After activating, the webpage shows only "Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 523800 bytes) in /home/u299823818/public_html/wp-includes/plugin.php on line 40".
Any idea?
I appologize if this issue has alread been addressed here.

Not really that important, but it would be nice to try to use it.

If you need any other info just ask.

Thank you very much for your attention!