I'm guessing that the format of your pictures has changed, or the way postimage stores or transporrts them.
Take care of the "width" parameter in the Insert Media function. 450 width is good for forum posts, while wall posts must be much smaller.
On your wall, I see that former pics are "scaled to 200 (width)" and fit well, while the last one is not scaled and appears too big. Thus, 200 may be the number!
Have fun!