Offenses involving contraband or smuggling are usually strict liability offenses, so mens rea is irrelevant in most such cases.

Even granting applicability of mens rea / actus reus analysis here, I believe your analysis is wrong. It's true that attempting to do something actually illegal and failing is often still an offense (usually of the "attempted" variety), but incorrectly believing that what you intend to do is a crime, when it actually isn't, does not automatically make that act criminal. For example, if you think jaywalking is a crime in a jurisdiction where there is no law against it, that will not in itself render your jaywalking criminal. That would be an absurd result.