Hmm, it sounds like we define "blocking error" as "corrupts the B2G profile". But that isn't what actually matters to app developers, whose primary concern is whether or not they can test their apps. And in any case profile corruption is the responsibility of the Simulator, not the app developer. It represents a bug in the Simulator rather than a problem with the app developer's manifest (whether or not the manifest is valid).

So I think we should focus the "blocking error" category on issues that prevent an app from being tested in the Simulator, whether or not the issues cause profile corruption. The "non-blocking error" category (which seems analogous to a "warning" in many error-reporting systems) can then represent other kinds of problems, like those that reduce the effectiveness of testing (no icon) or might prevent the developer from uploading their app to the Marketplace (which requires at least one icon that is 128x128, according to the [app manifest docs](https://developer.mozilla.org/en-US/docs/Apps/Manifest#icons)). Although I'm cautious about adding warnings, which often are more trouble than they're worth and cause developers to tune out all messages.