I tried closing Gnumeric and I had the same problem. Maybe DropN900 requires a minimum amount of change. Usually I make small changes to the worksheets in the N900. For example, I have a worksheet with a list of scientific journals and I fill in the issues I have browsed. That means I add a few digits at a time. I have tried with bigger changes and this triggered the synchronization. I am afraid now that it is a problem of the minimum threshold that DropN900 requires to consider that the file has changed. But this would be a matter of the DropN900 forum. If so I thank again the developper and the people in this forum for the quick response and the inconveniences.