215 ILCS 5/155.03

No company doing business in this State shall assert by way of defense or otherwise, in any suit, action or claim arising directly or indirectly out of the issuance or delivery of any policy or certificate of insurance, that such company was without capacity or power to issue such policy or certificate or that such policy or certificate is void, invalid or unenforceable because of such lack of capacity, if the coverage under the policy or certificate was afforded with the express knowledge or the consent or acquiescence of the company.