Q: On my Blackberry I get a "Device Error: 400" and can't get past it. What can I do?
A: This issue is related to the Blackberry device being out of memory. You can solve it by following these steps:
1. Disconnect Blackberry from your computer
2. Open "Desktop Manager"
3. Open "Application Loader"
4. Reset your Blackberry (small hole under the battery door)
5. While the red lamp is on, reconnect your Blackberry to your computer and click "Next"
6. On the following screen you will see either "USB:Unknown" or "USB:", click again on "Next"
7. Now you will see the list with the system applications for your Blackberry
8. Select the applications you need and click again on "Next". The firmware will be reloaded to your device, all data that is on your device will be lost
original link:
Device Error 400 - Swiss BlackBerry Forum