...That's not going to work, that's not even valid! *Slaps forehead* If it's Arial, you should already have that font on your computer! Else I'd go back to the link you got it from and see if they have a download link to the font you need.
The best thing I'd suggest though is to just search through the script and search for 'font' or 'Font' and either delete the line, or change it to something you have. Or, you could google the font name and that might help you out too.
If the script has something like...
Default.font_type or $defaultfonttype in it, just delete the damn lines, because that's remanent of the old PK Edition days and is not the way the 'legal' version of RPG Maker handle's the default font set.
If you need to change the default font, go into main and add these lines
Font.default_name = "Times New Roman"
Font.default_size = 22
etc.