is that cell (on your pc) linked to another file? if so, he needs access to that file as well. If the formula refers to values or cells on other worksheets or workbooks and the name of the other workbook ---you will need to correct this.
here are some other reasons:
This error occurs when Microsoft Office Excel doesn't recognize text in a formula.
Optionally, click the cell that displays the error, click the button that appears , and then click Show Calculation Steps if it appears. Review the following possible causes and solutions:
Using the EUROCONVERT function without the Euro Currency Tools add-in being loaded
The EUROCONVERT function requires the Euro Currency Tools add-in (add-in: A supplemental program that adds custom commands or custom features to Microsoft Office.).
Install and load the Euro Currency Tools Add-in add-in
Click the Microsoft Office Button , click Excel Options, and then click the Add-ins category.
Select Excel Add-ins in the Manage list box, and then click Go.
In the Add-Ins available list, select the Euro Currency Tools check box, and then click OK.
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Using a name that does not exist
Make sure that the name (name: A word or string of characters that represents a cell, range of cells, formula, or constant value. Use easy-to-understand names, such as Products, to refer to hard to understand ranges, such as Sales!C20:C30.) exists. On the Formulas tab, in the Defined Names group, click Name Manager, and then see if the name is listed. If the name is not listed, add the name by clicking Define Name.
Misspelling the name
Verify the spelling. Select the name in the formula bar (formula bar: A bar at the top of the Excel window that you use to enter or edit values or formulas in cells or charts. Displays the constant value or formula stored in the active cell.) , press F3, click the name that you want to use, and then click OK.
Misspelling the name of a function
Correct the spelling. Insert the correct function name into the formula by clicking Function Wizard in the Function Library group on the Formulas tab.
Entering text in a formula without enclosing the text in double quotation marks
Excel tries to interpret your entry as a name even though you intended it to be used as text.
Enclose text in the formula in double quotation marks. For example, the following formula joins the piece of text "The total amount is " with the value in cell B50:
="The total amount is "&B50
Omitting a colon (:) in a range reference
Make sure that all range references in the formula use a colon (:); for example, SUM(A1:C10).
Referencing another sheet not enclosed in single quotation marks
If the formula refers to values or cells on other worksheets or workbooks and the name of the other workbook or worksheet contains a nonalphabetical character or a space, you must enclose its name within single quotation marks ( ' ).
Opening a workbook with a call to a user-defined function (UDF)
A user-defined function (UDF) is called from the workbook but is not available on the client computer. A developer can implement a UDF in several ways. For more information, see Visual Basic help and the Microsoft Office SharePoint Server 2007 Software Development Kit (SDK).