You need to install a standalone Veeam Report Viewer to view offline reports.
Solution
There are several options to install Veeam Report Viewer:
Veeam ONE ISO file: You can start Veeam Report Viewer setup from the ISO file: VeeamONE_10.0.0.750.iso\Redistr\ReportViewer.msi.
Veeam ONE Reporter UI: You can start Veeam Report Viewer setup either using the Veeam ONE Reporter UI: Workspace > Offline Reports > Select any report > Actions panel > Download Veeam Report Viewer. Image may be NSFW. Clik here to view.
Veeam ONE Reporter URL: You can start Veeam Report Viewer setup either using the Reporter URL: http://ComputerName:1239/Viewer/VmReportViewerSetup.msi
Veeam ONE Reporter installation directory: You can launch the installer from the installation directory (the default path is C:\Program Files\Veeam\Veeam ONE\Veeam ONE Reporter Web\Viewer).
