From Mozilla x86-64

MT.EXE problem

On Windows 7 beta, you cannot build binaries well due to manifest problem. This is fixed by Windows 7 RC.

Although MT.EXE adds manifest (Side by side DLL dependencies etc) to DLL/EXE PE image, it will be failed like the following on some situations.

c:\Users\makoto\Development\mozilla-hg\objdir-win64\nss\mangle.obj
if test -f c:/Users/makoto/Development/mozilla-hg/objdir-win64/nss/mangle.exe.manifest; then \
        mt.exe -NOLOGO -MANIFEST c:/Users/makoto/Development/mozilla-hg/objdir-win64/nss/mangle.exe.manifest
-OUTPUTRESOURCE:c:/Users/makoto/Development/mozilla-hg/objdir-win64/nss/mangle.exe\;1; \
        rm -f c:/Users/makoto/Development/mozilla-hg/objdir-win64/nss/mangle.exe.manifest; \
fi

mt.exe : general error c101008d: Failed to write the updated manifest to the resource of file
"c:/Users/makoto/Development/mozilla-hg/objdir-win64/nss/mangle.exe". The binary is not a valid Windows image.

In Windows 7 Beta SDK release note, the following issue is written.

5.3.6 Problem Running mt.exe on Windows 7 Beta The use of mt.exe to add a manifest resource to a PE image file (.EXE, .DLL, etc.) that does not already contain a resource (.rsrc) section in it may fail on Windows 7 Beta. The problem does not occur on Windows XP, Windows Vista, and Windows Server 2008, nor does it occur on Windows 7 Beta when manipulating PE image files that already contain a resource section.

No way to build on Windows 7 beta. This is fixed by RC, so you replace with RC.