strangely enough, adding another datastore role works ok:
perl createRole.pl --rolename testrole --privileges "Datastore.Browse" --username root --server esxxxx --password xxxxx
Possible precedence issue with control flow operator at /home/j.asenjo/perl5/perlbrew/perls/perl-5.20.1/lib/site_perl/5.20.1/VMware/VICommon.pm line 2141.
Creating new role: "testrole" with the following privileges:
Datastore.Browse
Successfully created new role!