Build.ini constants

I have a build.ini file with the following constants
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[constants]
#OUTPUTDIR#=D:\DEVELOP\RELEASE
#SETUPNAME#=In_install_v4.1.2.exe
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According to the log, the constants are being picked up ok.
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> Constant set: #OUTPUTDIR# = D:\DEVELOP\RELEASE
> Constant set: #SETUPNAME# = In_install_v4.1.2.exe
> Constant set: _VER_MAIN = 4.1.2
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I'm guessing I'm going about this the wrong way. The output is not directed to this folder, nor is the output file name set from the constants.

Any help appreciated

Ron