Your use lib statement is incorrect. You only need to point to the top level of your library. So try

use lib "c:\PERL\lib";
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Perl uses the package name to find the location of the module. So, since you said the lib is c:\PERL\lib\crypt\blow fish\blowfish.pl, Perl is looking in c:\PERL\lib\crypt\blow fish\blowfish.pl\Crypt\Blowfish for the file Blowfish.pm. My question is did you download the module and add it correctly? If you used ppm, then the module should be in c:\perl\site\lib\. If you didn't use ppm, I would suggest trying that first next time. If you didn't use ppm, did you use nmake to build this module? It also would put the module in c:\perl\site\lib\. If you didn't use either, you better read the ReadMe again.