AI just made a birthday cake for my little girl...I used SMBC for the cake ..but many time it's turned to soup level and take too long about 2 hrs to get together as SMBC..and when comes to piping its watery drops..y? This things happened?

There are two things that can possibly be going wrong, either you are not getting your egg white/sugar mix hot enough or your butter isn't cool enough.  The egg white/sugar needs to get to 70-75 Celsius, the butter needs to be very cold but not quite straight out of the fridge cold.  I get the butter out first, cut it into cubes and leave it on the counter while I separate the eggs.  This seems to work fine except for extremely hot or cold days. If you don't have a candy thermometer it is very useful for something like this, it takes the guess work out of getting your egg whites and sugar to the right temperature.

I made smbc fine without a thermometer by just rubbing a little between my fingers. When it's not grainy anymore, you should be fine. Didn't take very long until the mixture was smooth.

AIt is possible that your meringue is not setting due to the introduction of fats during the whipping stage. Wipe your bowl and mixer blades with vinegar before letting them come into contact with your ingredients and see if you have better luck. When I first made SMBC, I expected it to fail miserably since I had heard so many woeful tales about it. But having made meringue for pies for many years, I habitually wipe down my tools with vinegar before starting and I think it makes a difference. I STILL expect my SMBC to fail ever time I make it, but so far so good!

I also wipe my bowl & blades with white vinegar before I start.  I use room temp. butter and heat the egg & sugar mixture to 160 degrees F and beat until stiff.  As long as I do these 3 things, It works every time.

I just started baking and pastry school and thats what they tell us to do. Never had a problem at home but depending on who is doing the dishes at school there could be residual grease...I have seen it fail for others who didn't follow instruction.

AAs I was falling asleep last night, it occurred o me that you had written something in your post about SMBC not coming together after two hours of beating and I wanted to pop back in here to check on that. If you are beating the mixture for that long, you very well may be breaking your meringue. Have you checked out Sweetapolita's blog post on demystifying SMBC? If not, give it a read. She does a good job of outlining the steps to take for a successful SMBC.

AMake sure your meringue is cooked prior to adding your butter.

Check out woodland bakery blog for a video and recipe. Her SMBC is a bit sweeter, but it's good. She has trouble shooting tips.

This is the tutorial I used when I first learned to make SMBC.  Short, talks about the the stages of SMBC with photos and entertaining all rolled into one.  Nowadays I cut the butter back some but the tutorial is great. 

http://fromscratchsf.wordpress.com/2011/03/08/tutorial-swiss-meringue-buttercream/

ATq ..

One trick is to refrigerate it for a couple of hours, then beat it with a flat bade until it comes together.