Hello Huhuan,
As my peers have mentioned, the issue is related to the system not detecting an image installed on the secondary partition.
To fix the issue please try installing 5.9.1 if you get the same error you may want to try installing an earlier version such as 5.9.0 (this upgrade process may have to be performed a couple of times until you see the firmware version listed on the secondary partition) then upgrade to 5.9.5. If the issue still persists, a last resort would be to try defaulting the AP to factory defaults then try 5.9.0 upgrade again.
The key for the upgrade is to get the system to display a version of WiNG on the secondary partition prior to installing another version.
Please let me know if this helps.
Thank you.
