@alepan If you get this error plus a popup saying "Projucer.app is damaged and can't be opened," it's probably a Gatekeeper issue. To fix it, open Terminal and paste in "sudo xattr -cr /path/to/Projucer.app" using the Projucer path from within the source code folder you're trying to use.
You might also want to run "sudo spctl --master-disable" to turn Gatekeeper off generally... I already had it off before trying to export so if the above doesn't work, maybe try that too.