The group is pursuing civil action against the Prime Minister Tuila'epa Sa'ilele Malielegaoi, various government departments and agencies, and the current and former attorney generals, Lemalu Herman Retzlaff and Aumua Ming Leung Wai, over the Land Titles Registration Act 2008.
It's challenging the constitutionality of the act, which allows the registration of customary land leases and requires the registration of all customary land in Samoa.
The group claims this violates articles 102 and 109 of the constitution.
The Supreme Court ruled that the former head of state has immunity under the Head of State Act 1965 and the bank under the Diplomatic Privileges and Immunities Act 1978.
The groups' lawyer, Unasa Iuni Sapolu, says the ruling will be appealed.
Meanwhile, former attorney general Aumua is seeking a strike out motion that is scheduled to be heard later this month.
The plaintiff is also facing an application by the Attorney General's office that it pay security costs of $US10,000 before the case can go to a substantive hearing.