At Valor Lakefront, a woman is worried because she can't find her suite key. She said she left with it at the 'reception desk', so going out the back entrance would help.
So, when you get out of the back door, use the radar app on the poketch or keep pressing the 'A' button around the back entrance to find the key.
(Hint, it is up to the left a bit when you first get out).
Go to this website and scroll down it might help.
http://pokemon.wikia.com/wiki/Pokémon_Diamond/Pearl_Walkthrough_(Part_6)
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right next to the back of the hotel in valor lake place
you get the white flute by findering the suite key at the valor lakefront
Go to the back of the hotel the second you get outside you should be able to find it using your item finder dowsing app.
there is no key for valor lake front
The key is somewhere just past the south entrance hidden on the floor so use the itemfinder to find it.