Windows Explorer crashes when opening network files

My client has 3 computers on a workgroup network. All of them are running Vista Business.
One of the computers is being used purely as a file server.
The others can connect to it and view/change files on the “server” but one them always crashes Windows Explorer when navigating away from the file or folder back to the root folder or elsewhere on the network.
The error message is “Windows Explorer has stopped working” the option is to restart explorer or stop it.
Any suggestions about the cause of this would be very welcome