Sending a message to a USB device using usb4java - Input/Output Error

I am trying to send a message to my USB device (Silicon Labs USB-UART Bridge) using this code:

public void sendMessage(UsbInterface iface, String message,
        int i){

    UsbPipe pipe = null;

    try {
        iface.claim(new UsbInterfacePolicy() {
            @Override
            public boolean forceClaim(UsbInterface usbInterface) {
                return true;
            }
        });

        UsbEndpoint endpoint = (UsbEndpoint) iface.getUsbEndpoint((byte) i);
        pipe = endpoint.getUsbPipe();
        pipe.open();

        int sent = pipe.syncSubmit(message.getBytes());

        System.out.println(sent + " bytes sent");
        pipe.close();

    } catch (Exception ex) {
        ex.printStackTrace();
    } finally {
        try {
            iface.release();
        } catch (UsbClaimException e) {
            e.printStackTrace();
        } catch (UsbNotActiveException e) {
            e.printStackTrace();
        } catch (UsbDisconnectedException e) {
            e.printStackTrace();
        } catch (UsbException e) {
            e.printStackTrace();
        }
    }
}//sendMessage

When I execute it:

public static void main(final String[] args) throws UsbException {

    Usb4JavaHigh usb4java = new Usb4JavaHigh();
    UsbDevice usbDevice = usb4java.findDevice((short) (0x10C4), (short) (0xEA60));

    usb4java.sendMessage(usb4java.getDeviceInterface(usbDevice, 0), "01FF05FB13", 0x81);
    usb4java.readMessage(usb4java.getDeviceInterface(usbDevice, 0), 0x01);
}

I get this Error:

javax.usb.UsbPlatformException: USB error 1: Transfer error on bulk endpoint: Input/Output Error
at org.usb4java.javax.ExceptionUtils.createPlatformException(ExceptionUtils.java:39)
at org.usb4java.javax.IrpQueue.transferBulk(IrpQueue.java:239)
at org.usb4java.javax.IrpQueue.transfer(IrpQueue.java:197)
at org.usb4java.javax.IrpQueue.read(IrpQueue.java:126)
at org.usb4java.javax.IrpQueue.processIrp(IrpQueue.java:76)
at org.usb4java.javax.AbstractIrpQueue.process(AbstractIrpQueue.java:104)
at org.usb4java.javax.AbstractIrpQueue$1.run(AbstractIrpQueue.java:73)
at java.lang.Thread.run(Unknown Source)

However I get no Errormessage for my readMessage, does anyone know a reason why this is so or has got a hint?

Thanks in advance!

Edit: The code works out when I change the Endpoint to 0x01 but that one is the EP 1 OUT, 0x81 is the EP 1 IN, so thats where I am supposed to send my messagesor not?

Edit 2: Code of readMessage:

public void readMessage(UsbInterface iface, 
        int j){

    UsbPipe pipe = null;

    try {
        iface.claim(new UsbInterfacePolicy() {
            @Override
            public boolean forceClaim(UsbInterface usbInterface) {
                return true;
            }
        });

        UsbEndpoint endpoint = (UsbEndpoint) iface.getUsbEndpoint((byte) j); // there can be more 1,2,3..
        pipe = endpoint.getUsbPipe();
        pipe.open();

        /*pipe.addUsbPipeListener(new UsbPipeListener()
        {            
            @Override
            public void errorEventOccurred(UsbPipeErrorEvent event)
            {
                UsbException error = event.getUsbException();
                error.printStackTrace();
            }

            @Override
            public void dataEventOccurred(UsbPipeDataEvent event)
            {
                byte[] data = event.getData();

                System.out.println(data + " bytes received");
                for(int i =0 ; i<data.length; i++){System.out.print(data[i]+" ");}
            }
        });*/

        byte[] data = new byte[8];
        int received = pipe.syncSubmit(data);
        System.out.println(received + " bytes received");
        for(int i =0 ; i<data.length; i++){System.out.print(data[i]+" ");}//*/

        pipe.close();

    } catch (Exception ex) {
        ex.printStackTrace();
    } finally {
        try {
            iface.release();
        } catch (UsbClaimException e) {
            e.printStackTrace();
        } catch (UsbNotActiveException e) {
            e.printStackTrace();
        } catch (UsbDisconnectedException e) {
            e.printStackTrace();
        } catch (UsbException e) {
            e.printStackTrace();
        }
    }

}

Yes Fidor is right 0x01 is for writing and 0x81 for reading. IN and OUT is from the perspective of the host controller.

You can read from IN endpoints and write to OUT endpoints. Only exception is Control Transfer which is direction independent.