I'm using vlookup(). When first entered, the formula shows the proper result.
If I edit the formula in any way like simply retyping a part of it, the
result of the vlookup() is no longer displayed, only the cell formula is
displayed. Even if I change back to the original "working" entry. Here is a
specific example: =VLOOKUP($E$1,'F:\DocumentControl\Documents\DOC-001-D
(MODEL_NO)\[DOC-001-D (MODEL_NO).XLS]MODEL_NO'!$A$3:$AZ$1200,2)
Originally the "col_index_num" was a cell reference such as "M2" to a cell
containing a number "2". When the cell reference was changed to the actual
number "2", the spreadsheet failed and the function cell showed the function
itself and not the result of the function. Changing back to "M2" didn't fix
the problem. Any innocuous edit seemed to cause this problem.