In 2010 Thawte decided to start signing “all certificates with an intermediate certificate that needs to be installed along with the SSL certificate.
Any certificate issued on or after this date requires the intermediate certificate to be installed.”
Accordingly, if you use a Thawte issued SSL Certificate, you probably need to download and install into your web server the “Intermediate_file” listed on the Thawte website.
The direct URL to this Intermediate Certificate of Thawte is: https://search.thawte.com/library/VERISIGN/ALL_OTHER/thawte%20ca/Thawte_SSL_CA_under_Premium_Server_CA.pem
In the Apache webserver software, the following line will enable the use of this file (if placed in the listed directory name) in your Port 443 VirtualHost config entries:
Any customers having Thawte Certificate problems are welcome to contact us for help.
FYI and regards,