html option in form_for errors

Hello, everyone:
     I tried the html option (multipart) to upload an image to
server , but the form_for always errors. If I remove the html option,
it works. I have no idea the reason, looks like it is only a syntax
error, but couldn't figure it out.
    Thanks a lot in advance!

Br,
Myst

Hello, everyone:
    I tried the html option (multipart) to upload an image to
server , but the form_for always errors. If I remove the html option,
it works. I have no idea the reason, looks like it is only a syntax
error, but couldn't figure it out.
   Thanks a lot in advance!

form_for([@task, @comment], :html => {:multipart => true})

Thank you ..... again, frederick.. now, I knows what stupid mistake
I've made