Thanks for tip. Although I tried it and it did not find my street.
We've been using Google Maps: http://maps.google.com.ar since it went live last year and its been very helpful and accurate. You can do driving directions also by clicking "Indicaciones" after you find your first address. The only complaint is that is does not have many business listings yet, but that is slowly changing. Tip: Enter addresses with "Capital". Eg. "Av Corrientes 400, Capital" to search within the city limits.
I came across the error message a few times, too. This site is very particular about street names - they have to be exactly right, or that nice little message pops up.
So far, I've been able to get directions every time I tried it. It even gets one-way streets right, something not easy in BA, where they keep changing.
The Buenos Aires interactive map posted above (http://mapa.buenosaires.gov.ar/) is also very good, but it is just for the Capital. Clarin's map covers the whole metro area - that's why delivery services use it.