1. serious illness
2. Death in family
3. Can't get out of country
1. Minor injury.
2. Minor member of band can't play who is easily replaced.
3. A better offer (i.e, big support slot, tv show, not enough ticket sales)
4. Need to finish album.
5. Drug habit.
Worse offenders are obvioulsy doherty and winehouse. NIN cancelling cos of injury to drummer's finger was also rubbish. Anyone else got examples?