All in-box INF files must be encoded as Unicode; they must not be ANSI.
To encode an INF file as Unicode (or to verify whether the INF file is encoded as Unicode), perform the following steps:
Use Notepad to open the INF file.
On the File menu, click Save As.
If "ANSI" appears in the Encoding field of the dialog box, change the encoding to "Unicode" and save the file under a new name.