i found a solution for me without a downgrade
first clear cookies in chrome/ other web browser (transmision www link etc 192.168.1.10//transmission/web/)
then login in to the wd nas and tunr off transmission
next turn on and wait a while, log off and log in to wd nas
should be a option to upgrade transmision to new version (from 1.15 to 1.16 via 3.0 )
but i lose all added torrents (task) that i recomend to copy all torrents from copy folder
