Post-archive validation failed: Invalid signature. The code object is not signed at all

Until yesterday, I was able to archive, check out and submit app projects. I'm not sure what went wrong, but now after zipping the project, when I run Validate, I get the message "Invalid Signature. The code object is not signed at all."

• I checked my build settings: on code signing, code signing identification, release is set to "iPhone distribution: xxxxxxx inc (ARV8ZG344B), and prvisioning, release is set to" iOSTeam provisioning Profile: com.xxxxxx. xxxxapp ".
• In the main schema, the archive build configuration is set for release.

Any idea what I should do to fix this?