While the error is a bit unknown I must clarify some things:
1. Excel is an application that requires desktop interaction unless specified else or using Tasks that perform background operations - like the Office Macro Task
2. As Excel by itself needs the desktop it will probably act strange when it is launched by the SYSTEM user (which VisualCron uses) on a desktop (0) where no one is logged in at
3. if you don't want to use the background Tasks for Excel you could try to set the Task to run in foreground (main settings of Task). Please try that.
I changed the execution environment to foreground, and the error message went away, but Cron's popup messages tell me that the task completed immediately after it started. No excel window appeared.
A task set up the same way to run notepad.exe seemed and the notepad window opened, so that worked. I didn't try to open a specific .txt file with the notepad, so the test is not quite the same as trying to open a specific .xls or .xlsx file.
I can type excel.exe as a "run..." windows menu item, and it starts excel, but if I put excel.exe in as a chron task to run in the foreground, no excel window opens.
Thanks for your continuing help,
George Wolfe