SBS Backup fails on schedule but works direct

Morning chaps.

I have an odd issue whereby SBS backup fails on its nightly schedule but if I click 'Backup Now' it works everytime...

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The log shows the following:

26/02/2007 23:00
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Date: 26/02/2007
Time: 23:00
User: SYSTEM
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Backup Runner started.
NTMS session started successfully.
EnumerateNtmsObject(NTMS_LIBRARY) succeeded.
Will enumerate on 4 media libraries found.
GetNtmsObjectInformation(NtmsLibraryInfo) succeeded.
GetNtmsObjectInformation(NtmsLibraryInfo) succeeded.
Found an enabled library.
InventoryNtmsLibrary(NtmsInventoryOmid) succeeded.
Identify Media completed
EnumerateNtmsObject(NTMS_PHYSICAL_MEDIA) succeeded.
Will enumerate on 0 media types found.
GetNtmsObjectInformation(NtmsLibraryInfo) succeeded.
Found an enabled library.
InventoryNtmsLibrary(NtmsInventoryOmid) succeeded.
EnumerateNtmsObject(NTMS_PHYSICAL_MEDIA) succeeded.
Will enumerate on 1 media types found.
GetNtmsObjectInformation(NtmsPhysicalMediaInfo) succeeded.
GetNtmsObjectInformation(NtmsMediaTypeInfo) succeeded.
Found a tape media type in the library (Ecrix VXA-1).
Launching NTBackup: ntbackup.exe backup "@C:\Program Files\Microsoft Windows Small Business Server\Backup\Small Business Backup Script.bks" /d "SBS Backup created on 26/02/2007 at 23:00" /v:yes /r:no /rs:no /hc:on /m normal /j "Small Business Server Backup Job" /l:s /p "Ecrix VXA-1" /UM
NTBACKUP LOG FILE: C:\Documents and Settings\SBS Backup User\Local Settings\Application Data\Microsoft\Windows NT\NTBackup\data\backup08.log
=====================<BEGIN NTBACKUP LOG FILE>=====================
=======================<END NTBACKUP LOG FILE>=====================
NTBackup finished the backup with errors.

For more information about failed backups, see the article on troubleshooting your backup at the following Web page: http://go.microsoft.com/fwlink/?LinkId=18414

Backup ended at 26 February 2007 23:33
Backup Runner finished.
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I can't actually see any errors in the above? the only thing the event log shows (Application log), at the same time as this is but may be coincidence:

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Event: 1524
Windows cannot unload your classes registry file - it is still in use by other applications or services. The file will be unloaded when it is no longer in use.  
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Thought I'd post here as it might be a simple solution before I 'rip into it' :)