Exporting a dashboard through the async API keeps the UI responsive during long exports.

Export without blocking.
Report = StiReport.CreateNewDashboard();
Report.Load("Dashboards\\DashboardChristmas.mrt");

await Report.ExportDocumentAsync(StiExportFormat.Pdf, "Dashboard.pdf");

How it works. The export runs asynchronously, so the form stays interactive until the file is written.
На скриншоте ниже Вы можете увидеть результат выполнения данного кода:

Exporting a Dashboard Asynchronously