Ok, just tried again with the same results...
I clicked on "All Data" underneath "Sync from iTunes."
Several songs say, "song being copied to song."
Then, I get several messages that say,
"song information being copied to song information
FAIL:C:\Documents and Settings\MyName\My Documents\My Music\iTunes Music\Unknown Artist\Unknown
Album\Song.wav"
This same message repeats for several different songs. At the end, only about 60 of my 1400 songs show up in WMC.