Like Joey S pointed out, could be something like that? It's something in your script that is the cause of this, not within VisualCron. Try to debug it within your script.
The script in question does not invoke anything on a remote computer, and the script completes all of it's tasks as expected. It does not throw an error outside of the VisualCron PowerShell task. I do not get the error when running it manually, so I have nothing to debug.
I tried creating an Execute task that ran C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe, passing the script and its parameters with the -File argument. It still worked fine, and this time no error appeared in VisualCron.