Hi. Thanks for the assistance. I will download the update manually as my plex says it is up to date on 1.9.7.4460.
I found the problem causing the conversion failed error in this thread. Conversion failed. transcoder crashed or failed to start up . The cause was a missing windows 10 update fix for a faulty update. Since I installed this update i had no more errors on Plex.
Just a pity i had to delete my plex library and loose al my metadata and already watched shows history and that was not the fix.