So simple. Thanks! I use a other browser with http://localhost:8200 and it works. Than clear the cache in the main browser and it works.
It is the same problem like the next thread „ Cannot install .deb on LinuxMint 22 Wilma. I have been using duplicati for about two years. After the new installation from Mint22 I had the same trouble. But I can’t remember exactly what I did to solve the problem. I probably installed version 2.09.x. It worked until I tried the update.
The paketmanager in Mint 22 say it is gtk-sharp3.
Correct but forgive me, I can’t remeber what was the correct version number.
I had download the version 2.0.8.1 and had try to install. And the massage was: „Can’t install. Missing: gtk-sharp2“ And it was ready with me 
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Thanks.
And great thanks for your help.