Storing default win32 ActivePerl perl in a directory called 5.10 will break @INC, see
How is the default @INC constructed?
$ perl\bin\perl.exe -le "print for @INC"
C:/tmp/ActivePerl-5.10.1.1006-MSWin32-x86-291086/ActivePerl-5.10.1.100
+6-MSWin32-x86-291086/perl/site/lib
C:/tmp/ActivePerl-5.10.1.1006-MSWin32-x86-291086/ActivePerl-5.10.1.100
+6-MSWin32-x86-291086/perl/lib
.
$ rename perl 5.10
$ 5.10\bin\perl.exe -le "print for @INC"
C:/tmp/ActivePerl-5.10.1.1006-MSWin32-x86-291086/ActivePerl-5.10.1.100
+6-MSWin32-x86-291086/5.10/lib
.