To prevent possible loss of data
excel cannot shift nonblank cells off of the worksheet
select another location in which to insert new cells,
or data from the end of your worksheet
if you do not have data in cells that can be shifted off of the worksheet,
you can reset which cells excel considers nonblank,
to do this press ctrl+end to locate the last nonblank cell on the worksheet
delete this cell and all cells between it and the last row and column of your data then save