Why is my iTunes match stuck on "waiting"?

[iMore Question]

I downloaded iTunes Match yesterday and a majority of my music library is greyed out and shows a "waiting" status for Match and will not play. Some of these songs are previously purchased and others are downloaded from CD's. I have tried updating Match and turning it on and off in iTunes but nothing has worked. How do I get my music back?

 

[kch50428]

Restart iTunes on your computer - and leave it running until Match can process your iTunes library.