get_userdata() issue

I have a website that is tied to phpbb & wordpress. I use the phpbb session to track my users site wide, which checks who they are and is they are logged in. Problem is, that the method runs a function called get_userdata() which seems to be also used by WordPress. The page results in a php error Cannot redeclare get_userdata() (previously declared in….wp-includes/pluggable-functions.php

I don’t want to modify anything in WordPress too heavily, and don’t want to touch phpbb at all, but I do need some kind of fix. Anyone have any ideas about this?