Hello.

Regarding the error 6411: The client side is reporting to you that the server is not shipping the data (or keep-alive messages) as quickly as it should. This is quite probably a problem on the server side, and it such case should be resolved there. In rare case, it could also be a problem on the client - for example, if the client process is overloaded and cannot cope with the frequency of the incoming messages.

The way to determine the root cause is to obtain the network communication captures (Wireshark) on the client computer, together with the client logs (form QuickOPC), and analyze them. If the network capture shows that the server is not shipping the as it should, you will need to resolve it with the server vendor (or it might be due to network infrastructure). If it shows that the server is shipping the data correctly but QuickOPC still report the error, we will need to look more closely onto the client side of things.

The instructions are here:
- kb.opclabs.com/Collecting_information_for_troubleshooting

If you have servers on multiple machines and huge amounts of communication, the Wireshark capture should, if possible, be configured to filter the traffic with just one IP address.

Before doing so, however, have a look at the CPU usage on the client computer, and at the CPU usage taken by the client process. If it is suspiciously high, it can be the reason. In such case, you might have reached the hardware limits. Also, checking the CPU usage on the server side similarly.

Regarding your other post where you seem to indicate the the Write call took quite long: It is not the same thing as error 6411, but in quite the same way, it indicates that either the server is taking so long to fulfill the request, or that the client is overloaded. In this case it will be even easier to tell "who is at fault", with Wireshark capture - simply showing the communication around that single Write call, and comparing the Request and Response message timestamps.

Regards