What were the weather conditions like at the time of application? It sounds like it wasn't setup properly. If possible let it sit in the sun, that will bake it on. Their website says to run your finger across a spot and if it smears then it is not properly setup. If it comes off perferctly, no smudges then it is ready to remove.
The clay bar and Z-6 are the only 2 products that shouldn't be applied in the sun. If you have any Meguiar's Quick Detailer, I would use that, save the Z-6 for after you use the Z-2. If you have any questions, you can go straight to the source, wet@zainobros.com I dropped them a question last night at about midnight, and had a response form Sal himself by noon today! Now how many business owners would take the time to reply to e-mails on the Sunday! Great product and great customer service, what more could you possibly want from a company?
Hope you get everything working for you, with a black car, Zaino is the only way to go!