I've inherited a partially setup Lync 2010 Group Chat implementation. When I try to sign into the Group Chat Admin Tool, I get a message that says "Cannot sign in because of an invalid certificate". I'm not really sure what certificate it's referring to.  The certificate on that chat server's IIS is valid and the certificates in the Lync Topology are valid too.

Where should I be looking?

Thanks

Hi,

From your description above, it can be the issue of certificate.

Please Issue a new certificate for Group Chat that contained no SAN entries and had an exportable private key.

Assign the new certificate to Group Chat via the Group Chat Configuration Tool and to the Group Chat web site binding for HTTPS.

Best Regards,

Eason Huang