I reseted both devices and setup an wds connection.
It works perfect, while connection via a lan cable to the wds router.
But the wds router is not broadcasting an SSID. To make sure that the wlan component is not damaged, I changed the mode to accesspoint and than I could see the router. But in wds mode there is no way to see it. Even tried changing the security to wep and giving it another SSID or trying to connect to it manually (act like it would not broadcast) doesn't either work.