Microsoft Office 2003
Trouble Shooting
Installing SP3 - Fails with error 0x51F
Use regedit to modify the following key:
[HKEY_LOCAL_MACHINE] /SOFTWARE/Microsoft/Office/11.0/Delivery/{90000409-6000-11D3-8CFE-0150048383C9} /CDCACHE
and change the existing value '2' to '0'
Downloading the update exe from Microsoft.com and manually installing works.
If you're then prompted for missing files, you have no option but to provide an install CD.
-- Frank Dean - 02 May 2009