Came in to find that the laser had tripped.  Error messages were as before.  Found that although I could
reset the laser I could not turn it on without rebooting the Beckhoff computer.  All the TwinCAT channels
were live and so on.  When the command was issued to turn on the pump diodes, the pump diode current(s)
did not increase.

    The crystal chiller displays "Error Flow - sensor 1", as before, even though the laser is up and
running.

    One other observation is that the mouse on the Beckhoff computer appears to be dead.  Whilst its LED
is on, moving the mouse does not move the cursor.  Not sure that the two problems are related but it
certainly doesn't help.