Two fairly complex sheets of mine still work - except for minor "#####" issues in some (mostly date) cells. But that is absolutely harmless, it is no indicator of invalid data, but a warning that the cell is too narrow to display the number (a frequent phenomenon with all Excel clones, and even within Excel across different computers, as the cell width does not change to suit another, wider typeface). Data invalidity must affect some particular subset of cell formats only - could you look up which are affected in your case?