I have defined 3 arrays using DefineNames:
Boys_11_12
Boys_13_14
Boys_15_16

I then have defined a Combo dropdown with the following choices:
Boys_11_12
Boys_13_14
Boys_15_16

When the user selects the Boys age group using the Combo dropdown, I then use the selection in an Index function:
Index(Boys_(one of the three),...)

I get an error when using the Combo dropdown, but it works fine when I type in the array name directly into the Index function. Its as if it knows the array when typed in, but not using the Combo dropdown. I created the Combo dropdown by typing in the array names into cells as text, then using properties select where the dorpdown text is.