Maintanance backup plan fail

Question

Hi all
I have a maintenance plan to backup ALL databases on everyday 11:00am. however it failed start from wednesday.
I see the log is so strange:
Executing the query "
declare @backupSetId as int
select @backupSetId = position from msdb..backupset
where
database_name=N'DB_A' and
backup_set_id=(select max(backup_set_id) from msdb..backupset where database_name=N'DB_A' )
if @backupSetId is null begin raiserror(N'Verify failed. Backup information for database ''DB_A'' not found.', 16, 1) end
RESTORE VERIFYONLY FROM 
DISK = N'H:\\DB_Backup\\DB_A\\DB_A_backup_201303132300.bak'
WITH 
FILE = @backupSetId, 
NOUNLOAD, 
NOREWIND
" failed with the following error: "Cannot open backup device 'H:\\DB_Backup\\DB_A\\DB_A_backup_201303132300.bak'.
Operating system error 32(The process cannot access the file because it is being used by another process.).
VERIFY DATABASE is terminating abnormally.".
Possible failure reasons: Problems with the query,
"ResultSet" property not set correctly, parameters not set correctly, or connection not established correctly.
 ===================================================================================
Executing the query "
BACKUP DATABASE [DB_B] TO  DISK = N'H:\\DB_Backup\\DB_B\\DB_B_backup_201303132300.bak' WITH 
RETAINDAYS = 31,
NOFORMAT,
NOINIT, 
NAME = N'DB_B_backup_20130313230031',
SKIP,
REWIND,
NOUNLOAD, 
STATS = 10
failed with the following error:
"Cannot open backup device 'H:\\DB_Backup\\DB_B\\DB_B_backup_201303132300.bak'.
Operating system error 32(The process cannot access the file because it is being used by another process.).
BACKUP DATABASE is terminating abnormally.".
Possible failure reasons: Problems with the query,
"ResultSet" property not set correctly,
parameters not set correctly, or
connection not established correctly
Finally, the backup file is created on the disk, and the log above is display on 11:00:31pm....why verify is process before backup finish?
the backup file date is about 11:14pm...
really has no clue.
wednesday night and thursday night got the same problem, and the same database.

Answer 1

I have check it's already exclude .BAK
that's really strange!!!!! Database DB_A has already been backup at 23:05:14...  Why it try to backup again on 23:09:42.....??
any how can I trace spid 54 to know what and who is doing ?
2013-03-14 23:05:14.94 Backup      Database backed up. Database: DB_A, creation date(time): 2011/02/02(14:14:54), pages dumped: 323851, first LSN: 156927:43:38, last LSN: 156927:59:1, number of dump devices: 1, device information:
(FILE=1, TYPE=DISK: {'H:\DB_Backup\DB_A\DB_A_backup_201303142300.bak'}). This is an informational message only. No user action is required.
2013-03-14 23:09:42.01 spid54      Error: 18204, Severity: 16, State: 1.
2013-03-14 23:09:42.01 spid54      BackupDiskFile::CreateMedia: Backup device 'H:\DB_Backup\DB_A\DB_A_backup_201303142300.bak' failed to create. Operating system error 32(The process cannot access the file because it is being used by
another process.).
2013-03-14 23:09:42.18 Backup      Error: 3041, Severity: 16, State: 1.
2013-03-14 23:09:42.18 Backup      BACKUP failed to complete the command BACKUP DATABASE DB_A. Check the backup application log for detailed messages.