[Plugin Nextgen] : WP MU integration, upload errors

Hi there,

I tried Nextgen image gallery plugins on a blog running on WP MU and got the following errors when trying to upload images…

ERROR: dosbook 002.jpg :
Fatal error: Call to undefined function: wpmu_enable_function() in /homez.63/brikabra/www/wp-content/plugins/nextgen-gallery/admin/functions.php on line 841

Then (despite confirmation that the upload was successful) :

Directory /homez.63/brikabra/www/wp-content/blogs.dir/6/files/1series contains no pictures

The files actually are on the server… yet the directory wasn’t created.
Anything to do with the permissions on the blog.dir (at the moment 755)?
Anyone with a possible solution?
This one is critical since i would like to be able to host photoblogs..

Thx in advance.
Annabel