I had Package preload failure on a 64-bit Windows 2008 Secondary site server the other day. The preloader would generate an exception and not function.
The long and the short of it was that we had the Preloader executable from the SMS2003 Toolkit still, and not the latest one. Once corrected the preloader functioned and did it's work.
You can down the ConfigMgr 2007 Preloader version here (http://www.microsoft.com/downloads/details.aspx?FamilyID=c36fcda8-9336-4d44-9568-5530ff7635dd&DisplayLang=en)
Old version: 1.0.3025.1000 (byte size 589,824)
New version: 1.0.3025.1100 (byte size 668,696)
Like us no doubt you will have toolkits on various network resources, and if like us you are a pure ConfigMgr environment then now may be a good time to purge the SMS2003 toolkit tools binaries and replace them with the ConfigMgr 2007 ones.
Wally Mead deserves a shout here for getting in touch with the developers to figure this out one for me. So obvious once the solution is staring you in the face