I've run into this so many times, especially the Maint Plan failing because it couldn't do integrity checks because a "user" was in the database. It then won't delete the old backups. I ended up putting the script below in a scheduled job that runs every 6 hours. Since then I haven't had a big problem with it.

declare @file_name varchar(100)

declare FileList cursor for
    select  physical_device_name
    from msdb.dbo.BackupMediaFamily bmf 
    left join msdb.dbo.BackupSet bs on bs.media_set_id = bmf.media_set_id
    WHERE  datediff(hh,bs.backup_start_date,getdate()) > 48 
    and datediff(hh,bs.backup_start_date,getdate()) < 168 
    and physical_device_name not like '%BEXVDI%'
    ORDER BY bs.backup_start_date desc

OPEN FileList
FETCH NEXT FROM FileList INTO @file_name
 WHILE (@@fetch_status  -1) 
  BEGIN
    --print @file_name
    SELECT @file_name = 'DEL ' + @file_name
    EXEC XP_CMDSHELL @file_name
    FETCH NEXT FROM FileList INTO @file_name
  END
DEALLOCATE FileList

Solved a lot of my major headaches.