I got a great recipe for italian meringue buttercream from the Whimsical Bakehouse (love the recipes in that book!) I've made it 3 or 4 times but my stand mixer was broke so I had to use a hand mixer and my husband's arm (what a sweetheart!). I finally got a new 7 quart cuisinart. Yesterday I went to make the buttercream using the whipping attachment(was that the right one to use?). It did not rise much after I put the boiling sugar and water in, then totally died after I put in the butter. I'm talking 2 1/4 cups sugar, 1 cup egg whites and 6 sticks of butter all organic $$$. Could not fix it no matter what. ent my husband to buy more butter. I started over again. Whipped up great until I added the butter, fell again. Used my hand mixer to get it a little thicker but still not the right consitency. I stuck it in the fridge I was so disgusted with it (after 10:00pm, had church this morning) Got up early re whipped it and the consistency was still just good enough for frosting the cake and writing happy birthday with some squiggles. 
Couldn't even do bordrers. I live in Dallas, very hot and humid this weekend. Was that what happened? Also any suggestions on wht to do with my first batch of "soup"?
Thanks,
Missy
I agree, if it was total soup it sounds like something (whether meringue or butter) was too warm. But then you're saying the second batch worked but was pretty soft even after refrigerating? So that leaves me a little stumped.
All I know is that once when I made IMBC it inexplicably turned to total and utter soup, so bad I COULDN'T keep whipping it as it was flying out of the bowl all over my kitchen. 15 min in the freezer...maybe 30...solved the problem. Actually then it was too cold so it curdled, but eventually the temperature got to the right spot and it all worked out, the cake iced perfectly.
It's hard to know for sure since you said you've made it successfully with a hand mixer...so the big question is, what changed?? When I use the KA I use the whisk until all of the butter has been added, and then I switch to the paddle. Antonia74's method on p3 of this thread http://forum.cakecentral.com/modules.php?name=Forums&file=viewtopic&t=404613&postdays=0&postorder=asc&&start=15 (lots more good info on this thread about IMBC!) Might be worth a read to see if any of her information matches/diverges from the technique you used, to help you figure what else might have gone wrong if it wasn't the temperature...
Mine always has an "ugly" stage but if I keep beating it eventually it gets there. Once my butter was too soft and my syrup/egg whites were too warm so I got soup too. I packed ice around the outside of the bowl and brought the temperature down, beating all the while. I was able to save it though it didn't have the volume it would have otherwise. Hopefully you'll get it figured out soon. (BTW, humidity could be an issue. I live in the Pacific NW and making divinity at Christmas time is always tricky because we're so wet here. If you have AC you could try cranking it up and see if it helps. )
You whipped the egg whites than added the 240deg cooked sugar right? I like to use a wet towel to help cool down the bowl after the sugar is incorporated. I always use the whip. My butter is room temp it's good, and soft, not melted, but soft. Every thing was good, and clean right. I always rewash everything when doing anything that has to do with egg whites. Did you separate your own eggs? If you did, any yolk? Yolk, or any fat will stop the whites from whipping.
Mike
I also helps to wipe the bowl and whisk or beater with a paper towel dampened with white vinegar, then dried before using.
The vinegar will remove any residual fats which sometimes cling to the bowl and beater or whisk, even after washing.
Theresa 
Yeah, I had the same disaster last week. Almost threw the cake across the room! It was the perfect consistency until I added a bit more vanilla and then I noticed a weird sloshing. Picked it up on my spatula and it fell off! Iced my cake and the icing slid down. So I threw the cake and the icing in the fridge and eventually got it to where I could somewhat smooth it but still didn't turn out nearly as nice as I'm used to.
It was so soft that I was terrified the cake would slide apart on my 3 hour drive home. Thankfully my bad luck had ended but even at RT I could tell something was wrong with it. At least it still tasted good. 
Oh, yeah, it was also 90+ degrees here all week and we had horrible humidity (in fact, we got hit by a storm so bad that night downtown Columbus was under 3 feet of water) so I also wondered if that was the issue.
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