Purchased songs from iTunes are greyed out, not playable, help!

After upgrading to iTunes 11, I found that all of the songs I've purchased on iTunes are greyed out and not playable, WTF!?

Has anyone else experienced this? Is there a solution?

I guess those were particular songs were the original purchased songs w/o the metadata having been edited.

If you see this cloud icon next to "Music," then iTunes Match has not been disabled:

In iTunes pull down Store > Sign Out. This will both sign you out of your iTunes Store account and disable iTunes Match. To sign back into the account Pull down Store > Sign In.