How can I count between two dates when format for the dates is DD-MM-YY

I need to know how many days are between 21/04/09 and 28/04/09

The solution should be 8 if I use =(A2-A1+1) but Im getting #VALUE!

Im used format = Custom = dd/mm/yy, also General and Number but they are
not working either.

Any suggestions?

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Juan Carlos