Please Help me with this one

Hi guys. i have a problem. i know it’s something easy but i don’t understand what i am doing wrong.

when i launch “site_nou.fla” i get in the output window something like this:

shape 4 has alpha [COLOR=red]NaN[/COLOR]
shape 3 has alpha 32.323
shape 2 has alpha 22.232
shape 1 has…

i don’t know why i am getting [COLOR=red]NaN[/COLOR] for shape number 4.

can u please tell me what i am doing wrong?