When working with array formulas in Excel, it is important to check for proper entry of the formula. This can be done by checking the following:

• The formula must be entered in all cells of the array.
• The formula must be entered as an array formula (i.e., using Control + Shift + Enter).
• If the array contains more than one column, the columns must be adjacent.
• If the array contains more than one row, the rows must be adjacent.

If any of these conditions are not met, the array formula will not work correctly.