Problem loading excel file from an applet in firefox (Office 2010)

892283

I load a signed applet in a web application.
The applet have to open a xls file. The scene is the next:
- Create the Workbook and the sheet of Workbook
- Open the Workbook:
String[] commands = { "cmd", "/c", "start","EXCEL.EXE", ROUTE_FILE };
Process proc = Runtime.getRuntime().exec(commands);

It works in all browsers (IE, Chrome, Safari...) except in Firefox.
(I test it with Office 2007 and it works, but now I've Office 2010 and it not works)

This is the error message in the java console:

Java Plug-in 1.6.0_27
Usar versión JRE 1.6.0_27-b07 Java HotSpot(TM) Client VM
Directorio local del usuario = C:\Users\user

----------------------------------------------------
c: borrar ventana de consola
f: finalizar objetos en la cola de finalización
g: liberación de recursos
h: presentar este mensaje de ayuda
l: volcar lista del cargador de clases
m: imprimir sintaxis de memoria
o: activar registro
q: ocultar consola
r: recargar configuración de norma
s: volcar propiedades del sistema y de despliegue
t: volcar lista de subprocesos
v: volcar pila de subprocesos
x: borrar antememoria del cargador de clases
+0-5: establecer nivel de rastreo en <n>+
----------------------------------------------------

java.io.FileNotFoundException: my_file.xls (Access is denied)
at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.<init>(Unknown Source)
at java.io.FileOutputStream.<init>(Unknown Source)
at jxl.Workbook.createWorkbook(Workbook.java:301)
at jxl.Workbook.createWorkbook(Workbook.java:286)
at mExcel.ManExcel.<init>(ManExcel.java:45)
at interfaz.Applet.init(Applet.java:78)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

Any suggestion?

Thanks in advanced,

Angie