HLOOKUP Can't Search by Lookup Value
 

I'm having trouble getting my Lookup Value to search. e.g.:

If the formula is:
=HLOOKUP(A1, B1:C10, 2, FALSE)

In one example if A1 = 01/01/2008. // HLOOKUP works great

If A1 is substituted for a formula which is equivilant to the date
(e.g. E1 or today()) // HLOOKUP reports that it can't find the
contents of A1 in the Lookup Range.

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How can I overcome this problem so HLOOKUP can search when the Lookup
Value contains a formula?