Can you be found guilty of committing a crime if you didn't know you were committing a crime?

People plead insanity to crimes. This is based on the principle the people must be able to comprehend that they are doing something illegal. Having said that, how can we apply the principle, "Ignorance of the law is no excuse"?

Traditionally, there have been more moral constraints than legal constraints; if something was "illegal", it would be "wrong", if a person just avoided doing "wrong" things, they would be all right. This doesn't hold true any-more, there are really obscure laws that carry very scary punitive measures.

This article, while being about US law, discusses several incidents that are make the point very well.

It's a long read, but well worth it.