im also getting the same errors when I visit other forum sites and i dont know why... thanks for the tip alokeseo..
Before you go redirecting these 404s to your homepage, have you checked the referring URLs? Do you know why they occurred? Don't shoot yourself in the foot; investigate and analyse why all these 404s. A 301 might not be the best way, especially as it's 10000. If you can provide more information.