Gray hairs. Get rid of one and seven more pop up in it's place.
This damn chocolate half sheet I'm trying to decorate is driving me NERTZ! The crumbs somehow are like flypaper, attatching themselves to my Viva towel. I look at it, it appears crumb free, and I use it to smooth my icing. But when I remove the towel....MORE CRUMBS!
I have a choice between throwing in my spatula or using it to commit hari kari. 
Relax.......breathe.......... go do some San Chin Kata.....come back....somebody will likely have some tips for you. (sorry, I don't know how else to help!)
HTH
PS. My loving Goju guy (DH) would like to know what the Kanji means in your avatar, if you don't mind my asking.
Chocolate crumbs are like...Gray hairs. Get rid of one and seven more pop up in it's place.
...ain't that the truth!!!!!!!!!!!!! 
I just started a thread yesterday asking for advice working with and icing chocolate cake because I often have the same problems! Some great tips were offered!
Here's the link to the thread. Hang in there!! 
http://www.cakecentral.com/cake-decorating-ftopicp-5933283-.html#5933283
I would say, make that layer of icing your crumb coat, get it fairly thin and as smooth as you can, let it sit and crust a little, then add another layer, the crumbs should not be such a problem then.
Oh, I had already done that. This was the final coat. No matter what, chocolate crumbs came to be attatched to my viva towel my static electricity or some other super secret voodoo method, even though I had carefully wiped down my table and every other crumb I could see. Every time I smoothed the frosting I'd find an area that had fresh crumbs. I wanted to cry. Or hurt something.
I ended up using a new towel every single time I had to change it's position. And my icing still isn't smooth, mainly on the sides of the cake!! I eventually gave up so I wouldn't hurt myself. I'll find a way to decorate them or write something over them. It just wasn't worth my sanity!
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