M. R. Civ. P. 61: Harmless Error.

Unless justice requires otherwise, no error in admitting or excluding evidence -- or any other error by the court or a party -- is ground for granting a new trial, for setting aside a verdict, or for vacating, modifying, or otherwise disturbing a judgment or order. At every stage of the proceeding, the court must disregard all errors and defects that do not affect any party's substantial rights.