In SQL7/2000 you can a look in the msdb table 'sysdbmaintplan_history' to see if there is a reason. Try that table.
(SQL 2000 Code)
select substring(database_name,1,17) as 'database', activity ,start_time as 'start', message from sysdbmaintplan_history where succeeded <> 1 order by database_name, start_time desc