Just did a fresh install of WordPress 3.1.3, added a StudioPress theme and acvitated Akismet 2.5.3.
I got the following error:
The plugin generated 176 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.
I deactivated and then reactivated and got the same error.