Had similar difficulties some time back. Its probably a Unicode problem.
To fix, open the aircraft.ini file in the aircraft folder, eg, for the Nieuport23 plane open the Nieuport23.ini file in the Nieuport23 folder (in the Aircraft directory), and use the option "Save As" to save it as an ANSII text file. It probably is an Unicode file and if so that would be the problem. If this works, do this for each aircraft ini file.
