Will not save

Hi,
We have a workbook on Excel which holds important information and has many
sheets to open with information in them. The worksheet will open fine and
will save fine as long as you only add information. If you try to move the
cell information to a different cell or delete a row/column, an error report
comes up after trying to save and any work dont after the colum/row move etc
will be deleted. We can not unbderstand why this is happening.

Please help

Sara