Windows 7 client is trying dot1x (PEAP) authentication via SSID, but is not working. For windows 10 client there is no problem authenticating to same SSID.
device model: AC6605
a. Configuration was verified and was well implmented.
-since for Windows 10 client dot1x was working, some setting had to be done on Windows 7 client.
b. Settings change on windows 7 client:
b.1. double-click on SSID -where dot1x problem exists
b.2. under "Security" tab, set the EAP type as PEAP
b.3. after changing to PEAP, click "Settings", under this dialog box deselect "Validate server certificate" and click "Configure".
b.4 under "Configure" dialog box, deselect "Automatically use my Windows logon name and password"
b.5. Click "OK"
This setting solved the problem, Windows Logon credentials were used automatically(domain name account), instead the account existed on radius server