Hi, I have just built a C extension. "python setup.py install" successfully builds the extension and puts the library , PGModule.pyd, in the Python23\Lib\site-packages folder. However, from within Python, "import PGModule" yields "ImportError: DLL load failed: The specified module could not be found" The setup.py file I am using looks like this: from distutils.core import setup, Extension setup(name='PGModule', ext_modules=[ Extension('PGModule', sources = ['PGfit_DataTypes.c', 'PGModule.c'], include_dirs=["E:\Program Files\GnuWin32\include","E:\sundials\includes"], libraries = ["libgsl"], library_dirs = ["E:\Program Files\GnuWin32\lib"]) ]) A few more clues/oddities: The extension uses the gsl (gnu scientific library) library. Without the "libraries" and "library_dir" flags, my code compiles fine but does not link (I get error messages like "in PGModule.o unidentified reference gsl_set_vector" etc). Other extensions that I compile from the same directory and using the same setup file, but minus the library flags, build fine and are importable and usable from within Python. When I look in the site-packages folder, PGModule.pyd is right there along with other modules (e.g. PGFit.pyd), yet "import PGModule" from a python shell yields the aforementioned error while "import PGFit" executes successfully. Any ideas? Thanks a ton, -mike