Frederic,I think I had the same problem with RC2 ("String index out of range: 5"). Possibly is has to do with the change in position format. I did set LATITUDE and LONGITUDE manually (with a texteditor) to "0.0" in configuration.xml. After that the program started and I could enter the correct values in the Preferences/UserData tab again.
But of course I don't know, if this "medicine" helps in your case. 73, Klaus DL4OAH