could not connect securely to server %2 because the certificate presented by the server was invalid. The certificate was ...

%1 could not connect securely to server %2 because the certificate presented by the server was invalid.  The certificate was not trusted as a server because the server Enhanced Key Usage (EKU) was not enabled for the certificate.

Resolution:
The network administrator has an invalid certificate installed on the server and will need to change the server's configuration to utilize a valid server certificate.  The server certificate is either missing the server EKU, or one of the issuing certificate authority (CA) certificates is not granted server EKU rights.  A blank EKU field in the certificate grants all rights, but if any issuer is missing the server EKU right, all certificates they issue aren't granted server EKU rights.

Conversations, you have %1!s! missed conversations. There are Exchange connectivity issues. Your conversation history cannot ... Could not automatically save your instant message conversation. To save manually, click Save As on the File menu of the conversation ... could not be added because your Contacts list contains the maximum number of groups or contacts.Delete one or more contacts ... could not connect securely to server %2 because the certificate presented by the server did not match the expected hostname ... could not connect securely to server %2 because the certificate presented by the server was invalid. The certificate was ... could not connect securely to server %2 because the certificate presented by the server was not trusted due to validation ... Could not connect to Microsoft Lync {0}, please ensure that this web page is in your list of trusted sites in Microsoft Internet ... couldn't be converted for presentation because Visual Basic for Applications (VBA) is not installed on this computer. Please ... couldn't be converted for presentation. Please restart PowerPoint and try again.If PowerPoint does not appear to be running, ...