Solution
The error you’re encountering occurs because the command is trying to set a string value but is unable to access the item. It is most likely because you are not referring to the property that you are trying to configure correctly.
As an example, referring to the above error image, the code below seems like it is intended to set the input file path of the Standard Input properties for the Call Executable step.
New_Step.AsPropertyObject().SetValString("StdInput", 0, "\"C:\\Users\\abc.exe\"")
To correctly specify the input file path, use
StdInput.Source instead of
StdInput. StdInput.Source represents the standard input string, expression, or file pathname.
For more information on the step type in the TestStand API, refer to the
TestStand API Reference help.