Upgrading Greenplum DB that includes PostGIS extension
My bet is that the postgis-ossv2.0.3_pv2.0.1_gpdb4.3orca-rhel5-x86_64.gppkg package has a bug and it does not have implemented the postupdate as defined in the Gppkg class. The TAG is optional (SPECFILE_OPTIONAL_TAGS = ... 'postupdate'] ) so it looks like it is calling 

Check if the upgrade script ($GPHOME/share/postgresql/contrib/postgis-2.0/postgis_upgrade_20_minor.sql) exists in that location. Package details.

From that specification:

PostUpdate:
10  - Master: "echo 'Please run psql -d mydatabase -f 
$GPHOME/share/postgresql/contrib/postgis-2.0/postgis_upgrade_20_minor.sql 
to finish the update.'"


Also, you may want to try the --clean option