perl -v

This is perl 5, version 26, subversion 0 (v5.26.0) built for MSWin32-x64-multi-thread 

# this perl has MCE support

 perl -MMCE -e 1

# and this is its path
PATH=C:\EX_D\ulisseDUE\perl5.26.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\c\bin;
C:\EX_D\ulisseDUE\bin\UnxUtils\usr\local\wbin;
C:\WINDOWS;
C:\WINDOWS\system32;


# this other one is 5.20.3 WITHOUT MCE

 perl -v

This is perl 5, version 20, subversion 3 (v5.20.3) built for MSWin32-x64-multi-thread

# original path

PATH=C:\EX_D\ulisseDUE\perl5.20.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\c\bin;
C:\EX_D\ulisseDUE\bin\UnxUtils\usr\local\wbin;
C:\WINDOWS;C:\WINDOWS\system32;

 perl -MMCE -e 1

Can't locate MCE.pm in @INC (you may need to install the MCE module) 
(@INC contains: C:/EX_D/ulisseDUE/perl5.20.64bit/perl/site/lib C:/EX_D/ulisseDUE/perl5.20.64bit/perl/vendor/lib C:/EX_D/ulisseDUE/perl5.20.64bit/perl/lib .).
BEGIN failed--compilation aborted.

# prepending the other version in PATH
set PATH=C:\EX_D\ulisseDUE\perl5.26.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\c\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\c\bin;
C:\EX_D\ulisseDUE\bin\UnxUtils\usr\local\wbin;
C:\WINDOWS;
C:\WINDOWS\system32;

 path

PATH=C:\EX_D\ulisseDUE\perl5.26.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\c\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\c\bin;
C:\EX_D\ulisseDUE\bin\UnxUtils\usr\local\wbin;
C:\WINDOWS;
C:\WINDOWS\system32;

# now... omg UPDATE: wrong assumption from my part: see below Anonymous Monk at 11144117

perl -MMCE -e "print $INC{'MCE.pm'}"

C:/EX_D/ulisseDUE/perl5.26.64bit/perl/site/lib/MCE.pm


##</code><code>##

set PATH=C:\EX_D\ulisseDUE\perl5.20.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.20.64bit\c\bin;
C:\EX_D\ulisseDUE\bin\UnxUtils\usr\local\wbin;
C:\WINDOWS;C:\WINDOWS\system32;
C:\EX_D\ulisseDUE\perl5.26.64bit\perl\site\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\perl\bin;
C:\EX_D\ulisseDUE\perl5.26.64bit\c\bin;

 perl -MMCE -e "print $INC{'MCE.pm'}; print @INC"

Can't locate MCE.pm in @INC (you may need to install the MCE module) (@INC contains: C:/EX_D/ulisseDUE/perl5.20.64bit/perl/site/lib C:/EX_D/ulisseDUE/perl5.20.64bit/perl/vendor/lib C:/EX_D/ulisseDUE/perl5.20.64bit/perl/lib .).
BEGIN failed--compilation aborted.


 which perldoc.bat

C:\EX_D\ulisseDUE\perl5.20.64bit\perl\bin\perldoc.bat