I have a wedding cake I am doing this weekend, and I am not wanting to waste my time or money on covering it with fondant. I decided to just ice the whole thing with IMBC and smooth it to achieve the smoothness like you would get with fondant. I practiced the cake a few nights ago and it went well until I saw it the next morning. The IMBC had cracked on top and the sides had little bumps all over them. 

Could this have happened from frosting the cake when it was frozen? Should I refrigerate the cake after the crumb coat instead to prevent condensation from forming? I usually do rustic cakes that have imperfect icing so this is a new one for me. Any tips are greatly appreciated! 

I've never used IMBC, so I have no idea.  It seems odd that your rustic frosted cakes do not have a problem.  Why would being smooth iced cause it to crack?  Maybe it was because it was frozen.  Hopefully someone with experience with IMBC can help.

I would say that it cracked because the layers were frozen. I work with chilled cakes and it's fine, but never frozen.  There was probably expansion as the cake thawed. 

The bumps are probably air bubbles. Without seeing it I can't be 100% sure. 

When working with either SMBC or IMBC, I always mix it with the paddle on the lowest mixer speed for about 8-10 mins.  This will help with air bubbles, but warming the BC will also help smooth it out. I usually use a propane torch on the bowl while it's mixing, or soften in the microwave for a few seconds and mix.  A stiffer BC is better to crumbcoat (then chill about 20 mins), and a softer one will give you a smoother finished coat. 

Also use a heated spatula or scraper on your final pass, it will make a big difference.

Thanks for the smoothing tips, rychevamp!  I need all the help I can get!

I'll second what rychevamp said and say that it's probably because the layers were frozen. SMBC is my go-to frosting, and I'm guessing IMBC behaves similarly. I always let the layers thaw before I stack them. I put a thin crumb coat on and refrigerate that for about 30 minutes, then do the final coat. 

i don't care for italian meringue bc -- i use swiss meringue bc and i always freeze my filled tiers and final ice them right out of the freezer --

italian has a funny texture to me -- but anyway -- it may or may not be because of the freezing although like i said i do it all the time with swiss, abc and french vanilla bc with no problems --