I just tried my own a large account, and reproduced the issue. I can suggest a work-around. It's about OK'ing sites to store and retrieve larger amounts of Flash player app data for your images and nothing else that's personal.. Default settings are small. But for accounts with lots of images, more space is needed.
Please try the following:
1. Ensure you have the latest Flash Player installed: http://get.adobe.com/flashplayer/ (today it's 10.3.181.34)
2. Then go to this web site which allows you to tweak Flash player settings on your own machine: http://www.macromedia.com/support/doc...
3. Select the site static.photoshop.com, and drag the slider to a larger value. I recommend 10MB just to keep things easy.
4. To be sure everything reloads OK, close and restart your browser and sign into your Photoshop Express account.
This worked for me, but please post back here if it doesn't work for you. And please post back here if it does, if only to let other users know.