Internet Explorer by default won't allow anything signed with an invalid certificate. You must manually go in and change the setting in the security settings "Initialize and script ActiveX controls not marked as safe for scripting" and either change it to prompt... or to enabled (very insecure)
Alternatively, if you can get the certificate for the activex control... and then add it to your root certificate authorities in the local machine... it would be able to identify the certificate as being signed.
Basically... the person who created the activex control either A) is using a bogus certificiate to sign his programs... or B) had a valid certificate but let it expire or it was revoked.
On a second though... Have you tried using a non-activex enabled browser? many programs like that have some detection built-in that will try activex... then fail-back to java or some such.