The motivation for this change is that PORTWRITEARRAY used to show a message which incorrectly referred to the first input when given a non-array second input. I could have instead corrected the text, but that would have left the non-English translations incorrect. This fix makes PORTWRITEARRAY act more like a typical FMSLogo procedure, throwing an error instead of displaying a dialog box that cannot be interacted with programmatically.
Since, after showing the dialog box with the incorrect message, PORTWRITEARRAY used to throw a "Stopping..." error, changing this to throwing a "Doesn't like input" error has negligable risk to backward compatibility.