The findValue parameter for the X509Certificate2Collection.Find(X509FindType, object, bool) method must be a string representing the issuer name of the certificate. This is a less specific search than that provided by the X509FindType.FindByIssuerDistinguishedName enumeration value. Using the X509FindType.FindByIssuerName value, the X509Certificate2Collection.Find(X509FindType, object, bool) method performs a case-insensitive string comparison using the supplied value. For example, if you pass "MyCA" to the X509Certificate2Collection.Find(X509FindType, object, bool) method, it will find all certificates with the issuer name containing that string, regardless of other issuer values.