Upgrade Zywall 110 Firmware

Vertimart_TD

Hi, 

We have configured our Zywall 110 to automatically upgrade the firmware version. But it fails with checksum error code: 400.

The running version is 4.39.  The versions I can download from https://portal.myzyxel.com/my/firmwares  are 4.65, 4.70 and 4.71 but in the release notes of version 4.65 they mention to upgrade to version 4.62 first. 
Where can we find this version and what are the best steps we have to take.

Thanks a lot. 

TD

Zyxel_Stanley

It is the same as this thread.