Can't send photos from iMessage on 3GS iOS 5

I just updated both my 3GS and iPod touch 4G to iOS 5. Both share the same iTunes account. I started iMessaging other friends using various iDevices (iPad 1, iPhone 4). The text messages send out successfully. But every time I try to send a photo from my 3GS, the progress bar just stops short of completion. After waiting for minutes, it just stays that way. I tried sending using my iPod 4G, and this time it was successful. I compared the settings of both iDevices and they're more or less the same. Is this an iOS 5 bug? Have other users experienced this? Your feedback is appreciated.