Lync 2010 client keep prompt for login

Hi,

I have a Lync 2010 environment and notice on couple users when they reboot their workstation they get prompted for their credential to login and it will keep prompting over and over until you have to click on cancel.  The Lync client works fine after you click on cancel but its annoying to keep getting prompt and its not accepting the credential.  Does anyone know how to fix this issue?

Thanks