Siemens tp170a modbus rs485

I have a siemens tp170a hmi and tried just for fun, to use modicon modbus driver settings and communicate with a regin roomcontroler. I use the IFB-port and change dip switches to rs485. I read temperature and some other input registers, works fine!
In my house i have 8 roomcontrolers with modbus and now I want to communicate with all of them. I use wincc flexible 2008, and added another modicon modbus connection with a different slave adress. But now I get errors when i generate the project. To many connections. Is it possible to have more than one connection like this to siemens tp170a?

http://w3.siemens.com/mcms/sensor-systems/SiteCollectionDocuments/wt/application_guides/milltronics/en/AG041612.pdf

I have not tried this but here is an application guide about setting this up using your HMI.

Hope this helps,

After reading the guide and some test in wincc I found that if I use TP177 i can use 4 connections. With TP170, only 1 connection. Probably because modicon use rs232, point to point...