When clicking on the scan icon of a scan batch, I expect the webscanning to open, but I get a file download dialog box instead.

The "Scan" button is found in front of the scanning batch.
The first time you start the webscanning, or a new version of the webscanning is available, a small program will be downloaded from the server.

Depending on the settings of the browser of the client, the program will be launched immediately.

Sometimes a file download dialog box opens instead. This means the user should download the program and run it manually.
After doing so, the webscanning application will be started.