Ask your host to change php memory limit to 128M and change the line in wp-config to match the limit.

In suhosin protected servers, php is not allowed to raise its memory higher than configuration.

I remember wp-admin tries to raise it to 256M which may cause lots of errors in suhosin log.

So after your host fixes it:
Code: 
define(?WP_MEMORY_LIMIT?, ?128M?);