Ok so on my third attempt at IMBC I got it nice and smooth and fluffy and it tasted sooooo good. I only made this for practice so I put it in the fridge for later on. When I took it out it was hard so I left it on the counter for awhile to defrost and when I came back it was curdled and soupy. What happened?
... but you can rewhip it and it will turn out the same as it did before you put it in 
Just whip it back up,it turns soupy and curdley because the butter melts when it warms up but it should whip up just fine!
I never have it turn runny and curdley when I leave it out to soften up, and I sometimes leave it out all night so that it's ready to use first thing in the morning. Was it really hot in your house? How long was it out? It doesn't sound like it softened up, it sounds like it melted.
I had this happen to me once. Just re whip it!!! It's like magic, it totally comes back together. Sometimes takes a little while, just when you want to stop the mixer to give up, it comes together. So keep it going until it comes together!!!
I use only SMBC, it happens to it too!! Does not happen on a cake. lol.
This is pretty normal with merique BC. You just keep on mixing it 'till it comes together. Rose Levy Biranbaum in her wonderful book The Cake Bible has great BC recipes. You can't miss if you follow them step-by-step.
Yep. I agree - it is like magic! Sometimes even when I'm making a batch, at first it seems like it won't possibly be firm enough. But then I whip the snot out of it, and voila! Beautiful, magical stuff!
Once I was icing a cold cake on a humid day, and I started having a problem with condensation - it was a mess! - I thought I was a goner - but I just scraped it off the cake and rewhipped it. I've been a SMBC devotee ever since.
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