Communicating whit a ModBus-compatible device

Hello all, 

I have seen a few topics on this question but so far none have managed to clear up the subject for me. 
I am trying to use a Logo 8.FS4 as a master/server for a project that is talking to other non Siemens devices. 
Right now I just have a value sitting in a register on another device that I am trying to read to get an idea of how it works but can't seem to read anything. 
I have set up a network project and placed in the Logo device and a "ModBus-compatible device" with correct addresses. From there I have tried connecting the two devices using the pins on the display, sending and receiving Network inputs and outputs and setting up Server and client connections on the Logo Pins (by pins I mean  the blue squares below the image of the Logo).  
I know there must be something simple I am missing but not sure what it is. 
 
Logo Details 
IP Address: 192.168.1.2
Subnet Mask: 255.255.255.0
Default gateway: 192.168.1.1

ModBus Device (Aspar MOD-ETH)
IP Address: 192.168.1.135
Subnet Mask: 255.255.255.0
Default gateway: 192.168.1.1

This device can only only values at 1000-1099, I Initially thought this would be a problem but the addresses the logo can look at seem to be free but it then stores in its own assigned. Is this correct? 

My apologies for the long post but wanted to be clear, 
Any help or advice would be very appreciated. 

Jack 

Thanks for your response

The register address is 1020, it is a holding register and the Unit ID is 2. 

The device I'm using is an RTU to TCP gateway and I'm using it in the way described in 10.2 of this manual. 

http://www.aspar.com.pl/katalogi/ETH_en.pdf

With that information can you see an issue with the attached image. 

Thank you.