Does AlphaVSS.x64.dll actually exist on your system? It should be located in the subfolder alphavss, under the Duplicati program folder.
The alphavss folder should contain 3 files: AlphaVSS.Common.dll, AlphaVSS.x64.dll and AlphaVSS.x86.dll.
It looks like something went wrong when copying the files of the last update to the Duplicati program folder. My suggestion:
- Download the latest Zip version of Duplicati.
- Stop all Duplicati instances (Duplicati.Server.exe, Duplicati.GUI.TrayIcon.exe, Stop Duplicati Windows service).
- Check in Task Manager if there are no running processes starting with Duplicati. If there are any, end these processes.
- Extract the contents and copy it over the current files in the Duplicati program folder. All files an be overwritten, you will not lose any data or settings.