SOLVED: Looks like a bug.  This happened to me when I tried adding individual folders (albums) to upload.  If I have a single folder then Music Manager uploads everything fine.

The way I got around it…

1) Create a folder for google music manager.  Example: “C:\GoogleMusicFolder”

2a) Either copy the music you want to upload into the folder

or

2b) Create links to the music you want uploaded.  (information on how to do this later)

3) You can write down the list you had already configured to upload.  My list was big so I decided to do this.  You can copy it from the registry.  The registry key is:

HKEY_CURRENT_USER\Software\Google\MusicManager\SharedMusicFolders

4) Configure Google Music Manager… On the advanced tab, set the “Location of my music collection” to point to your folder.

5) I also selected the folder in the upload tab.

Here is how I created links mentioned in 2b.  Start by opening a command prompt with administrator privileges.  (you can google it)

In the command prompt, I executed these commands:

C:

cd C:\GoogleMusicFolder

mklink /D “The Prodigy” “c:\Shared Music\The Prodigy”

That creates a link called “The Prodigy” to the directory “c:\Shared Music\The Prodigy”.  Google Music Manager will then see “The Prodigy” as a directory and proceed to upload all the music in it.

 

I hope this helps, it was taken from here:

http://productforums.google.com/forum/#!topic/apps/2Y7YpAV4uMA