and then what happened?

Either you made a typo, didn't save changes, or ... or ...

You can alway go the way of ENVironment varibles Re: One liner to config cpan to install all dependencies automatically along with temp modules?

Its Solved. I needed to use this option:

o conf prefer_installer MM

I saved the changes to cpan mbuildpl_arg and tried to run the cpan install once again but still getting the same error. I display the cpan version and it's taking the 0.008 version, not the latest version. The env PERL5LIB is set. The only thing that is strange is that when I do the cpan install for 'CPAN::Meta::YAML', it doesn't say that it is up to date like it does for other modules installed. It just installs it again.

# *** WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING ***
#
# The following REQUIRED prerequisites were not satisfied:
#
# CPAN::Meta::YAML version '0.008' is not in required range '0.011'


cpan[1]> o conf /mbuild/
$CPAN::Config options from /opt/app/d1cap1w6/.cpan/CPAN/MyConfig.pm:

    mbuild_arg         [--install_base /opt/app/d1car1m6/.perl]
    mbuild_install_arg []
    mbuild_install_build_command [./Build]
    mbuildpl_arg       [--installdirs=site --install_base=/opt/app/d1c
+ap1w6/.perl]
[download]

cpan[2]> o conf /make/
$CPAN::Config options from /opt/app/d1cap1w6/.cpan/CPAN/MyConfig.pm:

    make               [/usr/bin/make]
    make_arg           []
    make_install_arg   []
    make_install_make_command [/usr/bin/make]
    makepl_arg         [INSTALLDIRS=site INSTALL_BASE=/opt/app/d1cap1w
+6/.perl]
[download]

=> echo $PERL5LIB
/opt/app/d1cap1w6/.perl/lib/perl5:/opt/app/d1cap1w6/.perl/lib/perl5/x86_64-linux-thread-multi

=> perl -MCPAN::Meta::YAML -le 'print $CPAN::Meta::YAML::VERSION'
0.008