Yammer crashing on Windows 2008R2

Yammer is crashing with errors below when more than one user is trying to use it (working fine only for one user).

Problem signature:
  Problem Event Name:    CLR20r3
  Problem Signature 01:    yammer.notifier.exe
  Problem Signature 02:    1.0.0.513
  Problem Signature 03:    54454f1f
  Problem Signature 04:    System.Core
  Problem Signature 05:    4.0.30319.18408
  Problem Signature 06:    5231116c
  Problem Signature 07:    19eb
  Problem Signature 08:    131
  Problem Signature 09:    System.UnauthorizedAccess
  OS Version:    6.1.7601.2.1.0.16.7
  Locale ID:    2057
  Additional Information 1:    0a9e
  Additional Information 2:    0a9e372d3b4ad19135b953a78882e789
  Additional Information 3:    0a9e
  Additional Information 4:    0a9e372d3b4ad19135b953a78882e789