Record won't enable on individual channel strips

Has anyone encountered this problem? I went to set up a 24 track recording session and when I set up my tracks, the record button on the individual channel strips won’t enable. The signal is coming through from the DI; the record button just won’t activate…nothing happens when I click on it. The record button does work on the Transport, just not on the individual channel strips. Any suggestions?

Check they are actually assigned to an input?