When building using the VC6 DSP in Release mode it can't find the header
files because optional include directories is only set for the Debug
mode. I can't provide any VC6 files since I only have VC7 (if you want
a VC7 .vcproj file I'd be happy to help there, but whoever maintains the
VC6 portion may want to add the extra include directory to the .dsp).
-James