When melting chocolate why does it clump up instead of becoming smooth..
Sounds like your chocolate is seizing. This is due to poor temperature control. Have you tried using a double-boiler? This is done easily. Take a smallish pot, fill it with about an inch of water, bring to a simmer, not boil. Place a heat proof bowl on top, i.e. glass/metal. Place chocolate inside and whisk gently every 30 seconds or so until the chocolate is smooth.
Yes, how are you melting it? When melting in a bain marie, be sure that you keep the heat to a simmer so that steam doesn't billow up out of the pot and into your bowl. ;0)
Too, if you're melting it in a microwave, chances are that you're scorching it, which a microwave does extremely well. Once it has either seized (in the presence of water) or scorched, unfortunately you have to kiss it good bye and start over.