Let's try an analogy:
Suppose a police officer stated "I was walking along Coronation Road, when saw John Smith shoot Fred Bloggs" but the defence pointed out that the incident happened on Coronation Avenue and not Coronation Road, do you really think that a court would dismiss a murder charge because of the officer's error? Courts are not obliged to acquit someone just because of a technical flaw in the evidence.
The only way to challenge a fixed penalty is to appear before a court. The magistrate's would regard the incorrect address as a minor technical flaw. As long as they were satisfied that your untaxed vehicle was on a public road (irrespective of the name of that road), they would be certain to convict you. The fine would almost certainly be far higher than the fixed penalty, plus you'd also have to pay court costs.
Chris