I'm having trouble with my HLOOKUP.

=HLOOKUP(E7, 'DATA'!C2:X62, 5, FALSE)

The lookup_value (E7) is a reference to a date. The date format is
yyyy/mm/dd which is determind by the table_array.

I have changed the date by cell-formatting it so it appears 2008/06/23
(the cell is a a formula). This returns #N/A

When the lookup_value cell (E7) a direct reference to the lookup table
(='DATA'!C2) it returns the correct value.

Both methods appear as "2008/06/23".

Why when i type in a date (2008/06/23) does the HLOOKUP not return a
value?

Try with range look up as true.

=HLOOKUP(E7, 'DATA'!C2:X62, 5, TRUE)