What it means:

“#SPILL!” tells you that Excel was trying to update the results of a calculation that required multiple cells to display the results, but the cells it needed to use were not blank, so rather than overwriting the values, it reported the problem.

Typical causes:

Some types of formula in Excel produce results that can span multiple cells, rather than simply displaying the answer in a single cell. Dynamic Arrays, and the “Indirect” function are two examples that we use in models that behave in this way. For example, we use named ranges for results in combination with the “Indirect” formula to ensure that outputs end up in the right place in the Dashboard sheets to generate the charts. The formula is entered in a single cell (usually where the row label sits) and fills in values for every month to its right.

If you type in a value (perhaps entering an actual result or a note in the wrong place), and that gets in the way of any cell in the row being populated by “Indirect”, that will generate a #SPILL! error to alert you.

How to fix it:

Delete the value in the way, and everything will work normally again. Note that even a space or 0 could cause this error.