Currently Being ModeratedJan 29, 2012 9:24 AM (in response to CandiCoo)
If you haven't shut down iTunes and restarted it, you should try that. Also, you might want to try creating a new iTunes library, adding music to that, turning Match on (it is off by default for new libraries) and seeing if it will run on the new library. On Windows, you create a new library by holding down the sift key when launching iTunes.
If you have your music on an external hard drive, be sure that drive is turned on whenever you run iTunes Match.