Due to a bug the PhotoChooserTask
the PhotoResult.OriginalFileName
returns a temporary path only.
from msdn: "... This property would be useful for retrieving the chosen photo from the XNA MediaLibrary so that you don't have to save it separately in isolated storage. However, as of this writing, the OriginalFileName implementation does not behave as expected: it returns a temporary filename that is not useful for retrieving the photo from the XNA MediaLibrary class later. However, ..."
Microsoft encourages you to store and load the image within your app. (example: see article about Saving and Loading Data)
sorry for bringing that message to you.