Error with Match and Index formulas via a validation cell

excelproblem.xlsx

Hi all,

I am having trouble with my workbook (attached).
I have set out my problem in the workbook.

For some reason I can only lookup with a match and index reference with the first 4 dates of my data validation.
Every later date from 11/11/06 is showing up #N/A errors.

I hope I have explained enough in the example workbook.
I cannot put my finger on the problem. Help would be much appreciated.

Cheers Ollie