There is a problem with Postie 1.3.2 and WordPress MU.

On the blogs within my installation of WordPress MU, I would get this error when I went to the backend of the blogs that had Postie 1.3.2 activated:

Fatal error: Call to undefined function wp_get_current_user() in /<install path>/wp-includes/capabilities.php on line 920

The quickest fix was to use FTP to delete the plugin and replace it with the earlier version of Postie (1.3.1).  You can get it here:
http://wordpress.org/extend/plugins/postie/download/

I activated Postie 1.3.1 and everything seemed to be OK.

Now I just have to remember not to update the plugin until the issue is resolved.

Update: The text of the message is coming through, but it drops the subject.  It was adding “(via Postie)” until I deactivated the Postie Filter plugin. Anyone know why it’s doing this?  Please comment.