Consider the following scenarios.
You log on to Microsoft Lync Online by using Lync 2010 from a computer that does not have Microsoft Online Services Sign-in Assistant installed.
Lync 2010 displays a message that suggests you to download and install additional software (Microsoft Online Services Sing-in Assistant).
You ignore this suggestion, and then you wait for some time.
In this scenario, a credential dialog box appears that asks you to type your user name and password to connect and retrieve calendar data from Outlook.
You log on to Lync Online by using Lync 2010 from a computer that has Microsoft Online Services Sign-in Assistant installed.
You save logon password.
You delete the certificate that is issued by the Lync Online server.
You uninstall Microsoft Online Services Sign-in Assistant.
You try to log on to Lync Online again.
In this scenario, you receive the following error message:
There was a problem acquiring a personal certificate required to sign in. If the problem continues, please contact your support team.
Additionally, Lync 2010 does not display the message that suggests you to download and install Microsoft Online Services Sign-in Assistant.
To resolve this issue, install the following cumulative update:
2467763 Description of the cumulative update package for Lync 2010: January 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.