Node Manager Error

I am getting a Node Manager Error on some of my computers in the network and cannot seem to track the source or find a solution to the problem. All virus files are up to date and I have tried updates from Microsoft. The error causes the computer to loose connection to the network but only when the user tries to connect to our exchange server or other computers with shared files. I have been able to solve the problem by reloading the machine but doing that to 300 computers is really not something I look forward to. Any suggestions would be appreciated.