could not connect securely to server %2 because the certificate presented by the server was not trusted due to validation ...

%1 could not connect securely to server %2 because the certificate presented by the server was not trusted due to validation error 0x%3.  The issuing certificate authority (CA) for the server's certificate may not be locally trusted by the client, the certificate may be revoked, or the certificate may have expired.

Resolution:
A tool like winerror.exe from the Windows Resource Kit or lcserror.exe from the Office Communications Server Resource Kit can be used in order to interpret the error code listed above.  If you trust the server certificate, the issuing certificate authority (CA) certificate can be placed in the local trusted root certificate authorities certificate store.  If you have logged into the server before without issues the network administrator should carefully examine the certificate if no known configuration changes have been made.

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, ... Create a new Lync Meeting.The default options might allow uninvited people to join your meeting. Use meeting options to control ...