I have stored most of my music on an external hard drive. Now I am using iTunes match and each time I try to sync them it fails. The problem occurs ones you disconnect the hard drive and try to play a song out of the cloud. Each time I try to play some of the externally stored songs the file location is not found although it should be in the cloud! From other devices it also does not work, e.g. when trying to play via Apple TV I see the songs but they are not clickable. Can anyone help with a practical solution? I certainly cannot copy all my music back to my Mac, that would simply eat up all my storage.
This topic has been covered in-depth on this forum.
With iTunes Match enabled the location of the iTunes library does not magically change to being in the cloud. Your local library is untouched so iTunes is still looking for the local music files to play, which it can't find because the external HDD has been disconnected. If you wish to run with the external HDD disconnected and only stream from the cloud then you'll need to create a new, empty iTunes library by launching iTunes while holding down the Option key. Choose new library. Enable iTunes Match on the new library, let it do it thing. Once it is finished you will be able to listen to the music from the cloud.
As to the trouble with the Apple TV, I suspect the problem is that you are trying to play music via the Computers menu (Home Sharing) and with the external HDD disconnected the songs are not available. With the external HDD disconnected you'll need to use the Music menu to play your music from the cloud on Apple TV, or once you follow the above steps it will be streaming from iTunes, although that will be kind of redundant in my opinion.