It means that you have a script called "Pm For Lana", which uses one or more dialogs, and that the script isn't passing the correct parameters to the dialog on line 87.
You should never run a script from a course that you don't know and trust, or that you don't understand.
If this script has been published openly, please provide a link to the script, or show us the appropriate section(s) of the script so that we can look at it.
