Indiana Code Title 6. Taxation § 6-1.1-25-16

(1) the tract or real property described in the deed was not subject to the taxes for which it was sold;

(2) the delinquent taxes or special assessments for which the tract or real property was sold were paid before the sale;

(3) the tract or real property was not assessed for the taxes and special assessments for which it was sold;

(4) the tract or real property was redeemed before the expiration of the period of redemption (as specified in section 4 of this chapter);

(5) the proper county officers issued a certificate, within the time limited by law for paying taxes or for redeeming the tract or real property, which states either that no taxes were due at the time the sale was made or that the tract or real property was not subject to taxation;

(6) the description of the tract or real property was so imperfect as to fail to describe it with reasonable certainty;  or

(7) the notices required by IC 6-1.1-24-2, IC 6-1.1-24-4, and sections 4.5 and 4.6 of this chapter were not in substantial compliance with the manner prescribed in those sections.