"Symbol extraction process failed" with iPhone 3G

In the Organizer, when I try to use an iPhone 3G for testing, I get the error message "Symbol extraction process failed", with no further information on what I can do to fix this.

I've tried...

- Restarting XCode (I'm using XCode 4)

- Restarting device

- Resetting device (from itunes)

- Restoring device (from itunes)

- Upgrading firmware (was 4.0, upgraded to 4.2.1)

- Restoring device (from organizer)

This device isn't broken or functioning incorrectly in any (other) way, and I really need to test my app on a 3G.... How can I fix this?

Thanks in advance.