Avatars within plugins

Hi All,
I have been developing a plugin for a bit now but have stumbled across issues with avatars. I started developing the plugin in place in index.php and used get_avatar($userID,”40″) just fine, however when I then turned all this code into a plugin and place it inside my plugin directory etc, the get_avatar($userID,”40″) now doesn’t return anything.
I’m guessing that it needs some sort of global statement of some sort given that it’s moved into a function inside an directory that is not the base dir.
Any help would be greatly appreciated,
Cheers,
Sephers.