statfs /storage/sdcard0 failed, errno: 13

statfs /storage/sdcard0 failed, errno: 13

receiving this error in logcat with illegal argument exception
statfs /storage/sdcard0 failed, errno: 13
My code is
public double totalStorage() throws Exception {
**stat = new
StatFs(Environment.getExternalStorageDirectory().getPath());**
return ((double) stat.getBlockSize()
* (double) stat.getBlockCount());
}
Please help