Issue: Lync login credential pop-up.
Error message: Type your user name and password to connect for retrieving response groups.
When user login on Lync using their login credential they get login credential prompt with above error however valid credential will accepting. Same credential prompt will back again.
If we cancel credential prompt then credential pop-up will went away and Lync client will work as expected.
Specific to Lync 2010 client.
There are many reason behind it.
Verify the certificate you must have public certificate assign to web services on Revers proxy and VIP if available.
2. TMG / Reverse Proxy Authentication:
In my case - Credential pop-up issue is occurring due to authentication. We have TMG (Threat Management Gateway) where we published URLs.
a. Logged on TMG server.
b. On Lync Front End rule, right click and select properties.
Click on ‘Authentication delegation’. It was set “No delegation. And client cannot authenticate directly”. Which means authentication will happen on TMG level however authentication must happen on Lync server. That was the actual reason to get credential pop-ups, earlier TMG was checking credential
c. Have changed authentication to “No Authentication. But client may authenticate directly”.
After authentication changes users credential prompt for response group has stopped.