Unable to delete and close gap

[billhercus]

Creating initial video from 20 video clips.  After initial correct edits now unable to get 'Delete and Close Gap' function to work.  It is greyed out.  How can I get this to work again?

[billhercus · Accepted solution]

Found answer.  Need to delete outside track (e.g., music or narrative)  and then it is OK!