Two Thawte Certificates:

During the installation of Thawte certificates, an error may occur from time to time that the primary root is already present in the Trusted Root Certification Authorities.

You can see this in the Certificates snap-in of the MMC:

Delete the „thawte Primary Root CA“ certificate if you also find it under the „Trusted Root Certification Authorities“.

If the above case applies to you, please delete the certificate and insert the sent intermediate certificate in the corresponding section „Intermediate Certification Authorities“ in the MMC.