Errors when Copying References to External Cells

Kirk noted that if he copies a cell referencing a cell in an external workbook, he gets an error. However, if that external workbook is open when he does the very same steps, he does not get an error message. Kirk wonders why this occurs.

There could be a variety of reasons for this happening. The most probable is that for whatever reason the information that it must get from the external sheet is unavailable or cannot be located.

Another possible reason is that your formula could be an INDIRECT link or the workbook could have been opened and the links not updated. If the formula is complex, Excel requires that the external workbook be open. (Microsoft has never provided a clue as to what constitutes "complex" in this case. Basically, if you get an error, the formula is "complex.")

In general, you could consider a formula complex if it does a calculation on the external data to get a result, such as with MATCH, LOOKUP, etc. An example would be storing a month number in workbook A and using that value to calculate year-to-date costs from monthly data stored in individual cells in workbook B. (In other words, you use the month number as an index to access the information in workbook B.)

A workaround for some (but not all) situations is to do the complex calculations completely in workbook B with workbook B linking to workbook A to get the data needed for that calculation. Retrieving the month number from workbook A is not complex and can be easily done by Excel. You could then open workbook A and have it read the result of the calculation from workbook B.