When running & debugging an application on an iPhone / iPod using Xcode you get the error:
"A signed resource has been added, modified, or deleted."
With the application not being able to be redeployed until it is deleted from the device.
Simply turn off Passcode Lock on the device.
Update: This might just be an issue in the pre-release iPhone 3.2 SDK.
Update 2: If this doesn't work try:
- Xcode > Build > 'Clean' and then 'Clean All Targets'
- Xcode > Build > 'Build and Go'