Yep, that's the one... really pisses me off too. The only answer I've found (after a frustrating couple of hours on my n80 where I originally saw it) is to make sure that stuff that is going to be 'always on' is not installed on the memory card, i.e. Shozu, Messaging, etc. One thing I found worked ok, but not all the time, is to go in with Tasky or something else and kill the running task. So for example, there's a daemon for Shozu that's always running -- you can find it in the list, kill it, then do the mass storage thing. But this means you have to go in and re-initialize Shozu before you use it.
Frustrating!
-olly