Install OpenWrt on enterasys WS-AP3715i

Hi,

i try to install OpenWrt on enterasys WS-AP3715i.
I followed instructions on https://openwrt.org/toh/enterasys/ws-ap3715i
Booting TFTP Image works fine. Also download different upgrade images.

After running sysupgrade with an upgrade image (firmware upgrade as well as firmware snapshot) the access point stuck after Uncompressing Kernel Image ... OK

I tried with images from firmware selector as well as the original links from wiki.
What is the next step? How can I discover what is going wrong?

thanks in advance

best regards
Daniel