One of my Christmas presents was a 2GB microSD card for my T-Mobile Wing phone (a very nice Windows Mobile 6 device, extremely happy with it).  I thought it would be nice to sync some music to it so I could use it as a player.  So I attached it to my Windows Vista PC, went into Windows Media Player, and went to the Sync tab.  So far so good: it sees the device.  But it doesn't see the storage card (even though Explorer does), and the internal storage on the phone can't store more than a few songs.

After swearing at Microsoft, I remembered that I work for Microsoft - makes the swearing kind of pointless :-)  So I started searching for a fix, which led me to this KB article:

http://support.microsoft.com/kb/931621/en-us

One reboot later and problem solved.  One of these days Windows will proactively tell me about these types of things...