I've had problems automating Office from a Windows Service under Windows Server 2008, even though that works fine under Windows Server 2003. The problem also occurs at the Open call, so it may be the same problem.
I tried following the advice given by H Ogawa in this MSDN thread, and it seemed to work. It's bizarre, but kudos to Mr. Ogawa for discovering it.
Summary of the 'Ogawa Hack': create a desktop folder for the system profile, as:
C:WindowsSystem32configsystemprofileDesktop
and, if running on a 64-bit machine, create another one, as:
C:WindowsSysWOW64configsystemprofileDesktop
Also, the folder(s) need write permission for whatever user is "driving" Office.
[Edit: corrected link URL]
[Edit 2: clarified that on 64-bit Windows, you need both folders, not just the WOW64 one]
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…