[vi-admin@tancredi ~][http://everest.primp-industries.com|http://everest.primp-industries.com]$ ./updateVMPortgroup.pl --server everest.primp-industries.com --vmname "thegeneral" --vnic 1 --portgroup "production_network"
Reconfiguration of portgroup "production_network" successful for "thegeneral".

Update Network Adapter 2 to portgroup "test_network"

[vi-admin@tancredi ~][http://everest.primp-industries.com|http://everest.primp-industries.com]$ ./updateVMPortgroup.pl --server everest.primp-industries.com --vmname "thegeneral" --vnic 2 --portgroup "test_network"
Reconfiguration of portgroup "test_network" successful for "thegeneral".

Make sure you spell the VM portgroup correctly as it is case sensitive to your vSwitch configurations. To check, you can always run esxcfg-vswitch -l on the Service Console or using the vCLI.