Conifigure two networks with 4 Xbees

Hi Guys,
I have four XBees and I want to set up two separated Networks which are not interacting. Let's say:
XBee 1 is sending data to XBee 2. (both XBee PRO Series 1)
Xbee 3 is sending data to XBee 4. (both XBee Series 1)
My problem is that I receive some garbage with XBee 2 sometimes. The garbage just starts in the moment when I start the second network? Each Network on its own works perfect.

My Question is how to set Destination Adress, My Adress,..., to prevent the two networks to interact each other.

I read that MY Adress and Destination adress should be flip-flop for receiver and transmitter. So I tried this setup, but it's still the same problem:

XBee PRO Nr. 1:
Channel: 17
PAN ID: 1234
Destination adress High: 0
Destination aderss Low: 2222
My Adress: 1111
Scan Channels: 0040
Baudrate: 57600

XBee PRO Nr. 2:
Channel: 17
PAN ID: 1234
Destination adress High: 0
Destination aderss Low: 1111
My Adress: 2222
Scan Channels: 0040
Baudrate: 57600

XBee Nr. 3:
Channel: D
PAN ID: 4343
Destination adress High: 0
Destination aderss Low: 4444
My Adress: 3333
Scan Channels: 4
Baudrate: 9600

XBee Nr. 4:
Channel: D
PAN ID: 4343
Destination adress High: 0
Destination aderss Low: 3333
My Adress: 4444
Scan Channels: 4
Baudrate: 9600

But there are still transcription errors within XBee 1 and 2. (Means connection works, but some samples are just rubbish)

with the "Scan Channels Mask" the Xbees should be forced to scan only this singel channel and not to use other channels, right?

I'm using XCTU to program the XBees.
I tried a lot of combinations and I'm freaking out if I try some more...Can anyone help me?

Does each XBee have its own microcontroller? Are you using any other serial devices in your setup? Just checking to make sure you don't have serial data mixing together.

All of the channels, PAN ids, and addresses seemed ok to me. However, I've never messed with the scan channels property.

hi Tony,
XBee 1 is connected to an Arduino Nano which is reading the senor values. Xbee 1 is sending:
<value1/value2/value3/...> with 6 values
Xbee 2 is connected to an Arduino Mega, which is receiving these values.

Xbee 3 is connected to an Arduino Nano, too. But on the receiving site I'm only using an XBee to USB Adapter. So this XBee-connection simply replaces an USB-Cable. Arduino commands are send through the Xbee-connection and values are send back.

Do you think I could solve the problem, if I built the network with Xbee 3 and 4 in the same way than the first one? Means no arduino commands are send, only values in a one way connection.

Greetz
Daniel