Problem with communication Siemsns S7 - HMI

[bm1209]

Hello, I have an annoying problem with communication between Siemens S7 PLC and HMI panel. Here it how it looks like: I am using Siemens S7-315 with 343 Lean ethernet port. This port is used to communication with HMI terminal. Communication is realized through S7-TCP communication protocol. When I was testing the communication in the office everything worked fine and nothing wrong happened. The problem occururs only on the installation. After turning the PLC and HMI on everyting works fine, data is transferred correctly and variables are displyed on HMI. After a few hours the communication is suddenly lost. This is a direct connection between PLC and HMI and there are no other devices in this network. So it is not possible that suddenly there is an address confilct. I made a wireshark analysis (I connected a notebook and hub into the network) and I found out that when the communication is lost HMI terminal is trying to get data from the PLC but it is not responding. It looks like PLC ethernet port is broken. You cannot ping PLC from notebook and HMI. On the other hand you can exchange pings between HMI and notebook. The communication is back again only if you'll restart the PLC. The strangest thing is that I did not have any problem with the communication when I was testing it in the office. The configuration and project of PLC and HMI is excactly the same. The only difference is that on the installation PLC is realizing also a communication throguh Profibus and MPI. I've tried to use different ethernet cables (crossed, non-crossed) but in all cases the situation is the same. Do you know waht can be the cause of such behavoiur? Maybe someone had a similar situaion? In the attachment I send a screenshot from Wireshark which shows the moment when the communication breaks. Edited April 8, 2015 by bm1209