Hi all,

We have a Lync server 2010 and a Groupchat Server in our organization with about 100 users. 2 Colleagues having problem with logging in with groupchat client. They both get this error: Cannot Sign in because of an invalid certificate. Please contact your administrator. All the other 98 users don't experience this Cert error.

I really investigated this issue but can't find the solution.

What I allready did:

- recreated Groupchat certificates from the local CA and placed them in the Trusted Authorities on the server + client + added it to GP.

- Export my certificates with RUCT and installed them on the client

- Uninstall + Install

- Change the automatic login with manual inputs.

Can somebody help me please?

Under IE options can you uncheck the options for certificate revocation check . If this solves the issue. You may have to add the CRL or check for proxy in IE options. 

Hi,

Thanks for the repons, but it didn't help.