Microsoft communicator certificate problem in lion OS

Praviously when i was using mocrosoft communicator in snow leapord, it was running fine without adjusting any rpeferences... just clikcs after installation, i enter my credentials and it was all good to go.. i never faced any problems..

Now i enetered LION os.. and i installed office communicator and installed all updates and currently i run 13.1.3 in my LION os 10.7.4 ... now when i enter my credentials, i get a warning message.. saying :-

"either dat and time settings are incorrect or the digital certificate is not valid or installed on your computer. IF date and time are correct, see your network administrator to verify that your digital certificate file is valid and installed"

i have attached the screenshot of the above error in the attachments too... now i dono anything about these digital certificates and all.. when i tried browsing thru net over this issue, i saw that once people migrated to lion os almost all have this certificate issue... i tried understanding their language on the certificates., but couldn't understand.. can someone let me know how to fix this issue ?? how to do and what to do., in simple english in detaile