My organization is testing Lync 2013 server in a test environment. We are a small organization, so we are just testing using a single Standard Edition Lync 2013 server. We Lync-enabled four test users using the Lync Server Control Panel. My client machine was already automaticallly updated to Skype for Business 2015. When first launching, it auto-filled the user account as email@example.com. We used the SIP domain of our real organization when setting up the Lync topology as we weren't yet going to be using any voice features of Lync in the test environment, but we had to put something in.
When I changed the sign-in address to firstname.lastname@example.org, SfB was able to contact the Lync server and it prompted me for a username and password. I tried test\testuser, test.local\testuser, and even email@example.com along with the password for that user. Every time it says incorrect username or password, even though I am sure the password is correct since I'm logged onto the client machine with that account.
Do you have any suggestions as to where I might look to resolve this issue?