Songbird 1.3a: I can't get my MSC device mounted in Songbird. Why?

Hi
I'm running SB 1.3a under XP. I have a Sansa Clip MP 3 device in MSC mode.
For security reasons, I have deactivated all kinds of automatic execution when my MP3 device (or any USB key) is mounted in MSC mode, and the device simply appears as a disk in "My Computer".

I don't know if this is the reason, but the Sansa does not appear in MSC mode in Songbird, while I understood it should, by now.

Any hint?
Thanks
Olivier