Why is my ringtone greyed out

Just upgrade my iphone and itunes. My ringtone that I used on my iphone 3G is now 'greyed out' in itunes and

my 3 GS won't see it. I downloaded the app. 'Ringtone maker' and created a new ringtone, but it's still greyed out

in itunes. Please help - this is very frustrating!!