With function PERCENTRANK(array, x, [significance]):
If x < Min(array) or x > Max(array), the function will return #N/A.
In other words, you must have Min(array) <= x <= Max(array).

To deal with #N/A, you can use IF() to test:

=IF(MIN($A4:$A$2436) > 2, "Too Low", IF(MAX($A4:$A$2436) < 2, "Too High", PERCENTRANK($A4:$A$2436, 2)))

or

=IF(ISNA(PERCENTRANK($A4:$A$2436, 2)), "Out of range", PERCENTRANK($A4:$A$2436, 2))

or with Excel-2007+

=IFERROR(PERCENTRANK($A4:$A$2436, 2), "Out of range")

Replace "Too low", "Too high" and "Out of range" with whatever you want the function to return in those cases.