[plt-scheme] error install .plt file

This is from a new user tring to install mrmathematica:

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Here is the error message I get when trying to "Install .plt file"

setup-plt: Setup version is 350
setup-plt: Main collection path is /Applications/PLT Scheme v350/collects
setup-plt: Collection search path is
setup-plt:   /Users/krgue/Library/PLT Scheme/350/collects
setup-plt:   /Applications/PLT Scheme v350/collects
setup-plt: Unpacking DrMathematica from /Users/krgue/Documents/computing/scheme/mrmathematica/mrmathematica.plt
setup-plt:   making directory mrmathematica in /Users/krgue/Library/PLT Scheme/350/collects/
setup-plt:   unpacking doc.txt in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking info.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking installer.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking mathematica.png in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking mathematica.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking ml.c in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking tool.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking translation.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt: Warning: broken compiled/expanded code or wrong namespace; cannot find instance to restore imported renamings from module: |,/Applications/PLT Scheme v350/collects/mzlib/port|
setup-plt: don't know how to compile collection: mrmathematica

=================================

Disregard my previous email.  I just quit DrScheme, removed my /Library/PLT Scheme directory and tried again.  This time I got the output below.  It looks like I need to set an environment variable, but to what should I set it?

setup-plt: Setup version is 350
setup-plt: Main collection path is /Applications/PLT Scheme v350/collects
setup-plt: Collection search path is
setup-plt:   /Users/krgue/Library/PLT Scheme/350/collects
setup-plt:   /Applications/PLT Scheme v350/collects
setup-plt: Unpacking DrMathematica from /Users/krgue/Documents/computing/scheme/mrmathematica/mrmathematica.plt
setup-plt:   making directory mrmathematica in /Users/krgue/Library/PLT Scheme/350/collects/
setup-plt:   unpacking doc.txt in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking info.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking installer.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking mathematica.png in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking mathematica.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking ml.c in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking tool.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt:   unpacking translation.ss in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
setup-plt: Pre-Installing DrMathematica
extension-installer: can't find needed include files and/or library; try setting the environment variable PLT_EXTENSION_LIB_PATHS
setup-plt: Compiling .zos used by DrMathematica
setup-plt:   in /Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/
open-input-file: cannot open input file: "/Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/ml.ss" (No such file or directory; errno=2)
setup-plt: Updating /Users/krgue/Library/PLT Scheme/350/collects/info-domain/compiled/cache.ss
setup-plt: Done setting up
setup-plt:
setup-plt: Error during Early Install for DrMathematica (/Users/krgue/Library/PLT Scheme/350/collects/mrmathematica)
setup-plt:   extension-installer: can't find needed include files and/or library; try setting the environment variable PLT_EXTENSION_LIB_PATHS
setup-plt: Error during Compiling .zos for DrMathematica (/Users/krgue/Library/PLT Scheme/350/collects/mrmathematica)
setup-plt:   open-input-file: cannot open input file: "/Users/krgue/Library/PLT Scheme/350/collects/mrmathematica/ml.ss" (No such file or directory; errno=2)

=======================

Could anyone please help? Many thanks.

Chongkai
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