[Plugin: NextGEN Gallery] Multisite pagination / navigation issue

I will try to explain my problem as clearly as possible.

I set up a site with WordPress and got the NextGen gallery working fine.
The gallery is in the sidebar, on all pages, called from the template (not a widget).
The gallery displays 9 images, so there is a pagination.

Then, I set up the site as a multisite.

I have the gallery coming up on 4 different sub-sites (Gallery ID 1 each time).

Now, the Pagination doesn’t work anymore.

The link for PAGE 2 looks like:

http://domain.com/subsite/?nggpage=2&page_id=2

If I click on it, the page jumps to the Blog page and the gallery is still on page 1.

URL in the address bar looks like:

http://domain.com/subsite/?nggpage=2

If I click again on page 2, it gets worst.
It goes to the “Single” page of the blog article.

URL looks like

http://domain.com/subsite/2011/10/05/hello-world/?nggpage=2&pageid=1

But we are finally on the page 2 of the gallery AND the pagination WORKS, which means I can now navigate from page 1 to page 3 with no problem, except that we are not on the right page anymore…

Any idea? A problem in the htaccess?