Check the expiry date of your developer certificate, they only last 1 year and have to be renewed.
In XCode, go to the organiser and look in the subsections under the devices tab and make sure all of your certificates are valid.
If all of that looks OK, go back to the main view in XCode, and check the code "Code Signing Identity" in the "Build settings" for both the PROJECT and the TARGET, and check your have picked a valid identity for both the Debug and Release builds.
PS. This sort of error is not a problem with the Sparrow code is an XCode or certificate issue.