Final answer:
In Excel, the #REF! error indicates that a formula can't perform its function because it references a cell that is no longer valid. #EER is not a recognized Excel error code, and #### means that the column is not wide enough to display the data.
Step-by-step explanation:
Among the options provided, #REF! is the item that means a formula cannot perform its function in Excel. This error occurs when a cell reference is no longer valid because, for example, the cell it referred to has been deleted or moved. #EER is not a recognized Excel error, and the ! sign typically precedes a cell reference in a formula but does not indicate an error on its own. Finally, a series of #### in a cell usually indicates that the column is not wide enough to display the cell content, not an error in the formula's calculation.