Not possible to update or install WPMU plugins from the dashboard

Hi there!

I can't update or install WPMU plugins directly from my WP dashboard:

- in the regular WP "plugins" area, the WPMU plugins show the sign "upgrad to update"
- when I click on "update" in the WPMU "plugins" area, I'm always redirected to "download"
- update via remote on the WPMU site is not possible either

What can I do?

Thanks,
Alexander