Unsupported wallpaper

I tried creating wallpaper for impression with 240x400 pixel size in jpg format. When I try to open it in impression, I get "unsupported" message. Am I missing something here.

Thanks

It's 240x400 jpg. Any other option to select while saving it?

I can open it on my PC. I copied it to phone using usb cable & also sent it as mms msg. Both ways it didn't work.

Thanks

Wallpapers I download work fine. It's just this one which I created. I know there is something I missed. This is what I did -

10Megapixel (jpg) picture was cropped in ACDSEE editor & saved.
Resulting image was resized using Microsoft resize utility (where you right click the image and resize it) to 240x400 pixel. Resulting size is 22K.

I will try another jpg picture, in case there is something wrong with this one. And I did the whole process 2-3 times with no luck.

Thanks