A new trial will start on Monday for the Naitasiri chief, Ratu Inoke Takiveikata, after it was found one of the assessors was a soldier.
The retrial was into its second day in the High Court in Suva when his defence lawyer told the court a member of the Military Forces reserve force was one of the five assessors.
Justice Goundar ordered a mistrial and a new trial date was set.
Takiveikata was charged in 2001 for his alleged involvement in the mutiny at the army barracks on November 2, 2000 in which four soldiers were killed.
He was jailed for life in 2004 but an appeal in 2005 saw the Fiji Court of Appeal order the retrial that began on Thursday.