login problem on Wordpress

I installed Membership, watched wizard OK, then when I went to plugins directory I got a fatal error message
Fatal error: Allowed memory size of 41943040 bytes exhausted (tried to allocate 1024 bytes) in /data/20/1/2/11/1980174/user/2163170/htdocs/Investigate/wp-includes/capabilities.php on line 937

Now I get same error message when I try to login to the wordpress site