Hi, the black screen could hide a message writen in dark gray, can you check it? For example a database error.
You can try to put Newsletter in debug mode (see the main settings) and then check on status panel for a php error log (last elements of that panel). Check there if there are some kind of errors reported.
if the status panel report 40M it means WP is working with 40M. That could means you cannot change the memory limit can be a limitation of your provider.