Solution 1 : No mistakes in password, as suggested by others.
Solution 2: In the request seen on access_tracker check input tab >> connection : src_ip_address.
Make sure while adding the NAS to device list in clearpass you have used this IP address.
Example :
You have a NAS you access with IP 10.1.1 2 , but in the incoming request you see the source IP address listed as 10.1.1.3, then you need to make sure, while creating an entry for this device in clearpass >> identity >> devices, you used the IP 10.1.1.3