`get_error_message() on a non-object

Hello
I 've installed this plugin, on multisites
on the inscription page it lead to this issue :

get_error_message() on a non-object in /home/blueeyes/public_html/wp-content/plugins/signup-code/signup-code.php on line 155

I have no buddypress, and I use Mmebership, and I used only alfa-numeric caracters

Can you fix this issue ?