Media :: Will Not Update Transferred Mp3's

I have Moto Droid with the new 2.1 version. I am using Mixzing for me media player but I don't think this is a Mixzing problem but something with the Android platform or in the syncing process. I'm using Windows Media player to make play lists and sync to the Droid.

It worked great the first time. I had some mp3's on my sd card and Mixzing picked them all up. Now I wanted to add more and the new mp3's won't show up on my Droid even though it says they have synced successfully in Windows Media player. I don't know where else to look for them but they are not in Mixzing.

Could it be a Windows Media problem? I even looked for them through the media player that came with the Droid and it shows the first synced mp3's but not the ones I tried the second time.