"This panel can find nothing good as far as suitability factors go," said a member of the bench, John Peck.
Manson, convicted in 1971 and serving life for seven murders, has not appeared before the board since 1997.
"I've tried to take this thing that I do, that has become my lot in life, and make it have purpose," Ms Tate, whose sister was actress Sharon Tate, told the Associated Press news agency.
"I've been doing it for Sharon and the other victims of him for the last 40 years."
The wife of film director Roman Polanski, Sharon Tate was eight-and-a-half months pregnant when she was murdered by the Manson gang.