Error message when you try to sign in to Communicator or to Lync: "There was a problem verifying the certificate from the server"

Resolution for users

To resolve this issue, users should download and install the rootsupd.exe update. This update is available for download from the Microsoft Download Center:

Update for Root Certificates For Windows XP [February 2012] (KB931125)

Note This item updates the list of root certificates on your computer to the list that is accepted by Microsoft as part of the Microsoft Root Certificate Program. It does not allow for any optional configuration or GUI. 

To resolve this issue, Help Desk should download and install the new root certificate that is needed for affected users. The certificate is available for download from the following third-party website:

        https://www.entrust.net/downloads/binary/entrust_2048_ca.cer

Note This item updates the list of root certificates on your computer by way of a wizard interface.

To install the certificate, follow these steps:  

1. Open the certificate.  
2. Click the Install Certificate button.
3. When the Certificate Import Wizard starts, click Next >.
4. Select Automatically select the certificate store based on the type of certificate, and then click Next >.
5. Click Finish to install the certificate.
6. Click OK to complete the process.

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.