CM_PROB_UNSIGNED_DRIVER during HCK Test

We carry HCK test on our driver and encounter an error that seems contradictory.
The driver is not yet microsoft signed. The driver before passing the HCK test can’t get digital signature.
And the HCK test checks for signature and fails with CM_PROB_UNSIGNED_DRIVER.
My driver is signed with my company’s valid certificate.

Any pointers?

Regards,
Vidhya