Certificates installed after 6/27/2010 require additional installation steps.
Thawte is migrating its public root certification authorities from MD5, 1024-bit RSA keys to 2048-bit RSA keys. As part of this change, all Thawte SSL and Code Signing certificates issued after 6/27/10 will now be signed by an intermediate certificate that chains to a secure off line Root CA, instead of being issued directly by an online root. There is no need to replace your existing certificates; current valid certificates issued before 6/27/10 will continue to operate correctly and securely. However, for any new certificates issued after 6/27/10, web server administrators will also need to install the intermediate certificates using the instructions linked below.
For more information, see http://go.illinois.edu/070110
The link above contains a wiki page with links to the installation steps for popular server OS's and some material collected by IT Pros on campus who have already successfully completed the process. For questions, email email@example.com or leave a comment.