Backupscript erkennt manchmal Pools nicht korrekt

ERROR: The media "ACB5EA429A5B46AFAFA337317423DA94" is already allocated to another pool.   
ERROR: Backup process aborted, no data was backed up.

rem a batch script to perform a incremental backup

rem set some values first
rem the GUID of our Tape Library / Tape Drive
SET TapeLibGUID=060DA28570B947F4B5DB680A954EC3C2
rem the GUID of the "Free Media" pool  
SET FreeMediaGUID=3996979234374147B6A988B76125B944
rem the GUID of the "Unrecognized Media" pool  
SET UnrecMediaGUID=4DE170DEF31640B397F60B8BA74D8191
rem the GUID of the "Backup\incremental" pool  
SET IncrementalGUID=BF4FE3B10F994359B1EF22868135179C
rem The directory which we write our log files to.
SET OurLogDir=C:\Backup\log
rem full path to the backup selection file
SET BackupSelection=C:\Backup\Backup_i.bks

rem Determine the expected / desired name for the media
SET MediaName="Incremental %date%"  

rem set the name of our log file
SET logfile=%OurLogDir%\messages-%date%.log

rem The directory, where NTBACKUP will save its log files 
SET BackupLogDir=c:\backup\log

:start
rem force a library refresh
rsm.exe refresh /LG%TapeLibGUID%
rem rem wait for completion
sleep 30

rem determine the name and guid of the media inserted
FOR /F " usebackq delims==" %%i IN (`rsm view /Tphysical_media /CG%TapeLibGUID% /B /GUIDDISPLAY`) DO set medGUID=%%i  
FOR /F " usebackq delims==" %%i IN (`rsm view /Tphysical_media /CG%TapeLibGUID% /B`) DO set medName=%%i  

echo INFO: Incremental Backup procedure %date% started >> %logfile%

rem do we have a tape at all?
IF "%medGUID%"=="" GOTO NoMedia  

rem is the inserted media part of the "free media" pool?  
FOR /F " usebackq delims==" %%i IN (`rsm view /Tphysical_media /GUIDDISPLAY /CG%FreeMediaGUID% /B`) DO IF %%i==%medGUID% GOTO Free  

rem is it an unrecognized media?
FOR /F " usebackq delims==" %%i IN (`rsm view /Tphysical_media /GUIDDISPLAY /CG%UnrecMediaGUID% /B`) DO IF %%i==%medGUID% GOTO Unrecognized  

rem is the inserted media part of the "\backup\incremental" pool?  
FOR /F " usebackq delims==" %%i IN (`rsm view /Tphysical_media /GUIDDISPLAY /CG%IncrementalGUID% /B`) DO IF %%i==%medGUID% GOTO Incremental  

rem if none of the above, handle it appropiately
goto SomeOther

:NoMedia
echo ERROR: No media present in tape drive >> %logfile%
echo ERROR: Backup process aborted, no data was backed up >> %logfile%
goto end

:Free
rem Everything's fine, log and proceed  
echo INFO: Media "%medName%" taken from the "Free Media" pool >> %logfile%  
goto doBackup

:Unrecognized
rem Everything's fine, although media is unrecognized. Log & proceed  
echo INFO: Media "%medName%" taken from the "Unrecognized Media" pool >> %logfile%  
goto doBackup

:Incremental
rem Everything's fine, tape is rotating, log and proceed  
echo INFO: Media "%medName%" taken from the "Backup\Incremental" pool >> %logfile%  
goto doBackup

:SomeOther
rem Log that the inserted tape was in the wrong media pool and exit
echo ERROR: The media "%medName%" is already allocated to another pool. >> %logfile%  
echo ERROR: Backup process aborted, no data was backed up. >> %logfile%
goto end

:doBackup
rem start the backup process
echo INFO: backup process starting >> %logfile%
echo INFO: The inserted media "%medName%" is empty or already used for a incremental backup >> %logfile%  
echo INFO: It will be re-initialized as "%MediaName%" >> %logfile%  
echo INFO: It will be assigned to the media pool Backup\Incremental >> %logfile%
start /wait C:\windows\system32\NTBACKUP.EXE backup "@%BackupSelection%" /d "Set %date%" /v:yes /r:no /rs:no /hc:on /m normal /j "Incremental" /l:s /p "Incremental" /UM  

if errorlevel 1 goto backuperror

rem log success
echo INFO: backup process terminated gracefully >> %logfile%
goto endbackup

:backuperror
rem log errors
echo ERROR: backup process has thrown errors, inspect the backup log >> %logfile%
goto endbackup

:endbackup
rem log eject & eject
echo INFO: ejecting media >> %logfile%
rsm eject /PG%medGUID% /ASTART >> %logfile%
goto end

:end
rem determine the log file with the latest change
FOR /F "tokens=*" %%i IN ('dir /B /OD /TW "%BackupLogDir%\*.log"') DO set backuplog=%%i