Ok. I solved my problem getting back in the script and getting the parameter as double (feets) instead of string (meters). Then, I made a conversion and when exporting Excel loads the data perfectly. I give my post as solved. Thanks!
... {//Getting the width parameter. Autodesk.Revit.DB.Parameter p = window.Symbol.get_Parameter(BuiltInParameter.WINDOW_WIDTH); var widthFeet = p.AsDouble(); // Converting from feets to meters. var widthMeters = UnitUtils.Convert(widthFeet, DisplayUnitType.DUT_DECIMAL_FEET, DisplayUnitType.DUT_METERS_CENTIMETERS); ...