"Changing folder" error when selecting One Month view

When opening the One Month view an error box is displayed with the title “Changing folder” & an OK button. The view does open if you click OK & the other calendar views display with no problem. The error always occurs on the user’s PC but doesn’t do it when I open his calendar on mine. Both clients are 8.02 running on 7.0.3 server. Can anyone help?