Lync login error use self account without delete cache , but can login with others account anyway

Question

Greetings
I deployed Lync Server 2010 for my customer. it's running well for about one year.
but there are some users cannot login on lync these days. we tested the issue, the following is the test details:
   - only about 20% users cannot login on lync use themselves client computers.
   - when I delete the lync cache files at C:\Users\username\AppData\Local\Microsoft\Communicator
folder, they can login on once.  we must delete the folder next time when the user need login on.
   - we can use other user account to login on at the above computer anyway, need not the delete the folder.
would you plese give me some advice about this case.
Thanks
Frank@Hiweb 冯立超@瀚博资讯

Answer 1

Is this Desktop virtualization scenario? or do does user have roaming profile? Please ensure 
C:\Users\username\AppData\Local\Microsoft\Communicator
is excluded from AV scan and test 
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