Unattended Cross-Platform Installation Error (bootstr.dll)

I've ran into an issue doing a cross-platform install of Windows 7 x64 Enterprise from a 32bit PE (actually it's BartPE/XPE). Basically, I pre-partition the HDD prior to launching setup (so I don't end up with the 100MB reserved service partition), then I run the following command:

\\server\win7ent_x86_setup\setup.exe /installfrom:\\server\win7ent_x64_setup\sources\install.wim /unattend:\\server\setup\unattend.xml

I've mounted both the x86 and x64 iso images on the server, and shared them as win7ent_xYY_setup, so the entire DVDs are available to setup.exe.

So setup takes off and runs basically the entire initial file copy and just prior to the first reboot sequence, I get a pop-up:

setup.exe - Bad Image
The application or DLL C:\Windows\System32\en-US\bootstr.dll.mui is not a valid Windows image.  Please check this against your installation diskette.

If I click OK it, then I immediately get:

setup.exe - Bad Image
The application or DLL C:\Windows\System32\bootstr.dll is not a valid Windows image.  Please check this against your installation diskette.

If I click on that, then the installation carries on its merry way and finishes, then reboots into Windows 7 x64.

Now - I can understand why setup.exe thinks those are bad images - obviously those are the 64bit versions of the files. But the question is, why is setup.exe attempting to open them, and secondly, how do I avoid this from happening, because it is not really an unattended installation if you have to click OK twice in the middle of it.

dcc

Edited August 26, 200917 yr by dcolpitts