I'm having problems again installing Office 2007 on a localized Vista
Ultimate x86. The setup stalls and asks for Proof.cab.

The only trace I can find about this error in SetupExe(..).log is:

Executing chained package: Proof.es-es
04/19/2007 18:59:13 Installing chained package: Proof.es-es
PERF: TickCount=2340108 Name=Verify MSI local install source
Description=Begin function
OSE is detected as a registered service. Service binary is reported at
location: C:\Program Files\Common Files\Microsoft Shared\Source
Engine\OSE.EXE
OSE service binary is detected at location: C:\Program Files\Common
Files\Microsoft Shared\Source Engine\OSE.EXE
File at H:\Ultimater.WW\ose.exe has version: 12.0.4518.1014
File at C:\Program Files\Common Files\Microsoft Shared\Source Engine\OSE.EXE
has version: 12.0.4518.1014
Running OSE version 12.0.4518.1014
OSE is detected as a registered service. Service binary is reported at
location: C:\Program Files\Common Files\Microsoft Shared\Source
Engine\OSE.EXE
OSE service binary is detected at location: C:\Program Files\Common
Files\Microsoft Shared\Source Engine\OSE.EXE
File at H:\Ultimater.WW\ose.exe has version: 12.0.4518.1014
File at C:\Program Files\Common Files\Microsoft Shared\Source Engine\OSE.EXE
has version: 12.0.4518.1014
Running OSE version 12.0.4518.1014
OSE is detected as a registered service. Service binary is reported at
location: C:\Program Files\Common Files\Microsoft Shared\Source
Engine\OSE.EXE
OSE service binary is detected at location: C:\Program Files\Common
Files\Microsoft Shared\Source Engine\OSE.EXE
File at H:\Ultimater.WW\ose.exe has version: 12.0.4518.1014
File at C:\Program Files\Common Files\Microsoft Shared\Source Engine\OSE.EXE
has version: 12.0.4518.1014
Running OSE version 12.0.4518.1014
LIS: wait for package "{90120000-002C-0409-0000-0000000FF1CE}" to complete
caching
LIS failed to cache download "{90120000-002C-0409-0000-0000000FF1CE}-C"
resource "Proof.en|Proof.cab". Cache Error 0x80070017
Source Resolution succeeded
LIS: start caching file "Proof.en|Proof.cab"
LIS failed to cache download "{90120000-002C-0409-0000-0000000FF1CE}-C"
resource "Proof.en|Proof.cab". Cache Error 0x80070017

The CAB file is there, installing O2k7 on Windows XP (any language) works
flawlessly. Excluding all proofing tools from setup doesn't help.

What's going on here?