Members directory Plugin and categories Problem

Hello, I'm having a strange problem with "membership directory plugin".

Using wpmu/wp 3.1 with Nelo theme all updated to current.

Categories get "broken". I have permalinks set to "Month and name" and category base is "articles". when I activate the member plugin, the category archive pages become 404.

If I reset permalinks to "default" then categories come back, but then I get these errors:

members directory page - Members » Invalid User
Member not found.

and blog directory page - "Invalid page"

Any ideas? thank!