C.R.S. § 32-11-640

(1) Within the fifteen days immediately succeeding the publication of the assessment resolution, any person who has filed a complaint, protest, or objection on specific grounds in writing, as provided in this article, has the right to commence an action or a suit in any court of competent jurisdiction to correct or to set aside such determination. (2) Thereafter all actions or suits attacking the regularity, validity, and correctness of the proceedings of the assessment plat, of the assessment roll, of each assessment contained therein, and the amount thereof levied on each tract, including without limitation the defense of confiscation, shall be perpetually barred.