Tatyana,
I'm not sure if this applies to you, since you didn't mention what type of PC you are running, but I have the same problem with all of my PXI machines.
I have finally tracked the problem to this. All of the PXI machines on our network get the same IP address assigned by the network router. So when you try to connect to that IP address, the router does not know which one to connect to, and you get the error. If I have only PXI machine running, I can connect without problem.
Our network people here have not been able to figure out why they all get the same IP address. This should not be possible. They are still working on the problem. I've contacted NI about this also, but they have never seen it either.
I hope this gives you a place to start looki
ng. If you do find this to be the problem, and some one figures out how to correct it, please let me know so I can get mine fixed.
Good Luck
Ed