nova boot - 'ascii' codec can't decode byte 0x8b in position 1: ordinal not in range(128)

I am trying to launch OpenStack instance as follows

nova boot --config-drive true --image "image_vm" --flavor "vmname" --nic net-id="1b73b819-9b7c-4f34-ae58-c0e66014769b,v4-fixed-ip=XYZ" --nic net-id="66737f7b-ff0e-45ef-b5ec-48f25539aa33,v4-fixed-ip=PQR" --file /opt/vm-metadata.tgz=/root/vm-metadata.tgz "vmname"

This results into an error -

ERROR (UnicodeDecodeError): 'ascii' codec can't decode byte 0x8b in position 1: ordinal not in range(128)

I am running on OpenStack Platform 6 ( or Juno ).

I tried with
LANG=en_US and LANG=en_US.UTF-8

Any help will be appreciated