Tariq,
This happens to me when my dashboard is complex (more data connections/components/excel logic) and when the file goes corrupt.
I save the xlf file in local, close Xcelsius and open the dashboard again to publish it on the BOE or Platform.
(Note - This method doesn't work when the dashboard's fully corrupt. You may have to roll back to the previous versions to the point where the xlf is not corrupt)
~Bala