Error when running report as scheduled task

When attempting to run a Sage Intelligence report (Sage 100) via the Windows Task Manager, the scheduled task fails with the message: 

Native Error Number: [-1147121340]
Source Library: []
Error Text: [Sage 100 ERP Intelligence Reporting cannot create the report. Microsoft Excel is not currently installed. Install MS Excel.]

Of course, MS Excel is installed (Excel 2013). I can run the report directly from the Report Manager. What might be causing the error when using the Task Scheduler?