Minn. Stat. § 508.28: LIMITATION OF ACTIONS.

No decree of registration hereafter entered, and no original certificate of title hereafter issued pursuant thereto, shall be adjudged invalid or set aside unless the action in which the validity of such decree, or of the original certificate of title issued pursuant thereto, is called in question, be commenced, or the defense alleging the invalidity thereof be interposed, within six months from the date of such decree. No action or proceeding for the recovery of any right, title, interest, or estate in registered land adverse to the title established by any original decree of registration hereafter entered shall be maintained, unless such action is commenced within six months from the date of such original decree. No action or proceeding for the enforcement or foreclosure of any lien or charge upon or against registered land in existence at the date of any original decree of registration hereafter entered, and which is not recognized and established by such decree, shall be maintained, unless such action or proceeding is commenced within six months from the date of such original decree. No such action or proceeding shall be commenced by any person who is bound by the decree. Nothing herein shall affect any rights already barred when this law takes effect.