When a trust becomes irrevocable, the trustee must send a notice to all beneficiaries warning them that they have 120 days to bring any action to contest the trust.  (Prob. Code 16061.7.)  The 120-day limitation period for bringing an action to contest the trust is codified in Prob. Code 16061.8, which applies to any action challenging the validity of the trust.  No matter what its label, if the suit in substance challenges the trust it is subject to the 120-day limitations period.  Here, an action against those benefited by a trust amendment for fraud and forgery of the amendment was a contest of the trust barred by section 16061.8 because none of its claims could succeed unless the court found that the trust amendment was invalid.