When I first installed Mute Screamer it seemed to activate OK. I went on to make settings and save them. Following that I made some edits to my active theme and the site crashed, leaving me with a generic 404 at my URL and 'A WordPress error occurred' from my login screen.
Deleting the plugin folder from wp-content/plugins restored the site to operation.
I tried reinstalling the plugin from a fresh download and had the same site crash occur.
I had a look at the DB and noticed that there were a couple of entries in the intrusions table. I deleted the table from the DB. I am reluctant to reinstall the plugin to test it again.
There may be some interaction between another plugin 'Login Logger', 'Login Lockdown' and Mute Screamer. I have tried various combinations of these plugins, but it seems the problem is localized to Mute Screamer.