i have a problem on excel formula like following:

='Sheet-A'!B56

the problem is, it will not display the value of 'Sheet-A'!B56 in a special
cell which in another sheet. the cell has been copied from itself once.
before then, everything ok, it show the value of 'Liquor-List'!B56. but after
copied from itself, it just disply "='Sheet-A'!B56". other cells which not be
copied still ok. anybody has any suggestion?

Thanks.