Dual Wield

I have found that I can't wield a dagger named Icepick and dual wield Fang at the same time. I get the message that Fang is too heavy to dual wield with Icepick. Yet I am able to dual wield a black hammer or a silver longsword with an iron horseshoe pommel with Icepick. Both of which are significantly heavier than a fine elvish dagger named 'Fang'.