when and why does the shared excel history gets corrupted?

i 'm getting an error like :the change history for this workbook is corrupted .unless the workbook is removed from shared use,excel may not be able to load the workbook.and you will be unable to save any changes or remove the workbook from shared use later.if you remove the workbook from shared use the change history will be lost but you will be able to recover the data.save the woorbook and share it again.


why did the shared history get corrupted...one of the operation i performed before this was copying some data from excel 2010 to excel 2007.
i'm even having some other errors after this.the file was giving error like: "unable to read file"