Problem to save to text with rasbperry windows 10 iot uwp?

[Ken Ekholm]

I have problem with this visual c# uwp code when I am trying to save to text file with raspberry pi 3 with Windows 10 IoT.
var path = @"urls.txt";
var folder = Windows.ApplicationModel.Package.Current.InstalledLocation;
var file = await folder.GetFileAsync(path);
var lines = await Windows.Storage.FileIO.ReadLinesAsync(file);
(lines[0]) = textBoxRadio.Text;
(lines[1]) = textBoxRadio2.Text;
await Windows.Storage.FileIO.WriteLinesAsync(file, lines);

Following error message appears
Unhandled exception at 0x75DC0D6F (twinapi.appcore.dll) in blinky.exe: 0xC000027B: An application-internal exception has occurred
(parameters: 0x038CF1D0, 0x00000001). occurred
and the application halted.

Can someone help me?