Hello, the problem is solved !!!
Thanks for all who tried to help. I want short explain why this error appears to help others:
The problem that the PNG file could not be created was the result of an ITEM / THING relationship
- Thing was discovered by Paper UI with OH 2.2
- Item was created by hand ( text file, coming from OH 2.1, here it worked)
The channel was wrong.
in ITEM file (fault config):
Switch NAME “NAME” { channel=“network:**device:**192_168_178_32:online” }
After new discovery it must be ( running config):
Switch NAME “NAME” { channel=“network:**pingdevice:**192_168_178_32:online” }
So it looks like, that there was a difference between OH 2.1 and OH 2.2 for the network channels
The new discovered thing with the network binding is a ping device, former a device.
Regards