>>I would hold off. When you do call to follow-up on the interview, be very careful which words you use. Mike's recommendations were good ones - you want to stress your interest but you also don't want to seem impatient or desperate.
>
>I got an e-mail with a negative response due to the lack of knowledge in this area of business. I don't know how can I convince that person that I'm capable of learning any kind of business in a very short period of time...

IOW, they were hit by a guy who managed to convince them that he knows their job just as well as they do, and they took him (or her). May be someone who really does know it, or may be just a good artist. They'll see.