Custom Fade Filters

I have a 800 by 600 custom fade filter made, I saved it as a TGA and put it into the wc3 directory, imported it into my map, and put it into a trigger, it doesn't work when i play the game though. Is there something I am not doing? when I try to convert it to BLP through Wc3 Image Extractor it does a Run time error

any help would be appreciated.

You probably forgot to change the alpha channel of it in photoshop.

Go in channel, then press new and "color" all to black(if there was already an alpha channel, just color it instend of creating another).