Only ONCE in Wilton classes did I successfully pull off the technique of buttercreaming the cake...letting it dry...then using parchment and a spatula to smooth out all the wrinkles...

In class...it worked PERFECTLY. But since then, I've never been able to do it. What is wrong with my buttercream??

I add meringue powder and use little milk...still...my buttercream sticks to the parchment paper EVERY time, ripping it off the cake.

Moreover, my buttercream CRACKS. Its almost like a shell forms on the outside but even after a hours of drying, it is STILL liquidy on underneath that shell and the slightest movement causes cracks to form all along the top...

How can I solve this problem?

Sounds like you may not be allowing the icing to crust enough.  Also, if the parchment you're using doesn't have a silicone surface, it can stick. Personally, I prefer to use computer paper or a Viva paper towel.

As for the cracking, it can be from not enough fat or moisture in your recipe, flexing of the board under the cake [because the board isn't thick enough], or the cake shrinking under the icing.  After crumb coating, if you allow the cake to rest at room temp at least overnight you can minimize the shrinking issue.

I had not considered that maybe my parchment was the problem...how do you know if it has the coating? Can you recommend a brand?

I let the cake sit overnight and the icing still ripped off the next day...so I'm not sure if timing could still be a factor.

A paper towel?! Tell me more! I would think the pleats would leave indents? And the towel would pull up moisture??

AIf you let the icing crust and use a viva paper towel it smooths it. Viva paper towels have no pleats or markings on them

I use Viva paper towel and a fondant smoother. Works wonders every time. :)

Yes, ONLY the Viva paper towels mentioned above.  I prefer the printed Viva towels [no, the printing doesn't come off on the icing] because, for some reason, they seem to work the best.

As for the parchment, you can google search for silicone parchment, but Wilton's is fine:

http://www.walmart.com/ip/20552619?wmlspartner=wlpa&selectedSellerId=3&adid=22222222227014935146&wl0=&wl1=g&wl2=c&wl3=14105962750&wl4=&wl5=pla&wl6=35024069710&veh=sem

Can't leave the cake sit so long and then try to smooth it--with anything.  With a crusting BC, you need to use the parchment/Viva/computer paper no more than 10-15 mins. after applying the icing.