I've tried to copy over the whole dvb mediaclient package from raybuntu's release, but I'm getting the same error also with this.
So I'm pretty confused what is the problem.
In the link from below also a similar topic was found...
Interesting is that the mediaclient works, can lock to a frequency, but otherwise I'm getting the error
DTV_CLEAR failed [e=Success] and the strem won't start...
So if I'm using the same binary package from Raybuntu's build, where the tuner is working, I guess it has to do with something missing from the kernel itself.
However, I've read that Sundtek has only the USB part in the kernel space, the rest is in user space.
The tuner is recognized and visible in tvheadend.
I've also tried both 4.2 and 4.3 version with the same result.