"Von NotHaus used the Liberty Dollars in lieu of actual minted US coins and was found guilty on several charges stemming from making, processing, and using the imitation coins, the FBI said. He also was charged with conspiracy against the United States. "

This is technically the crime that he committed. You can't issue coins which are attempting to imitate U.S. currency

"The FBI claims that NOFRED “intended for the Liberty Dollar to be used as current money in order to limit reliance on, and to compete with, United States currency.”"

It is NOT illegal to create a competing currency. However, this is the real reason they charged him and brought him down

"“While these forms of anti-government activities do not involve violence, they are every bit as insidious and represent a clear and present danger to the economic stability of this country,” said US Attorney Anne M. Tompkins."

This is a completely spurious argument