It looks like it is a problem with node-red-contrib-iiot-opcua. You might be better to raise an issue there.
Are you trying to monitor/read the same tag multiple times?
No, I just imported my XML file (OPC UA data model) into Node-RED and could see the nodes as node js objects. For the first time, it was successful. When i shut and restarted the server of the node red, its showing the error.
Thank you very much, will do that.
I have resolved this issue. There was a problem installing the npm directories, I uninstalled completely and re-install,now everything works fine.