When you have many email addresses associated with your user account, you cannot sign in to Microsoft Lync 2010 for iPhone or Microsoft Lync 2010 for iPad.
This issue occurs because the size of the Live ID token in the web ticket that is received from the Web Ticket Service is larger than the maximum transport request size. This is because the account contains many email addresses. Therefore, the Lync 2010 for iPhone or Lync 2010 for iPad client sends a web ticket without the SOAP body.
To apply this change, install the following cumulative update:
For Lync 2010 for iPhone:
2721062 Description of the cumulative update package for Lync 2010 for iPhone: June 2012
For Lync 2010 for iPad:
2709412 Description of the cumulative update package for Lync 2010 for iPad: June 2012