Custom Action in Wix Installer

All,

I developing a Wix installer that calls into a DLL to execute a custom install action. When I run the installer I get the following error in the event log:

Product: GB-X Volume Shadow Copy -- Error 1723. There is a problem with this Windows Installer package. A DLL required for this install to complete could not be run. Contact your support personnel or package vendor. Action _CustomAction_Install, entry: MSIInstallAction, library: C:\Program Files\GBVss\GBVSSSETUPHELPER.DLL

At this point the DLL is completely stripped down and only calls OutputDebugString(). I can see that the DLL's main entry point is being called for Process Attach/Detach -- so it appears it knows how to find the DLL. The dll is in the right location. MSIInstallAction is in fact the right entry point name.

I'm using Wix 3.0 and i trying to install on Win 2008 32-bit.

Does anyone have any ideas?
Thanks,
Dale