what is the correct consistency for cream cheese frosting

My current favorite cream cheese frosting recipe comes from Thomas Keller's book Under Pressure - page 218. The proportions of the major ingredients include:

cream cheese: 100%, butter: 68%, sugar: 132%

Your recipe uses:

cream cheese: 100%, butter: 24%, sugar: 80% (using the maximum recommended amount).

It may be that you just need a lot more sugar (or more sugar and butter), or it may be that the cheese being sold in your part of the world is not the "cream cheese" we know of here in the USA.

A fabulous cream cheese frosting recipe that stays firm enough to pipe. 125g butter at room temp, 150g cream cheese straight from the fridge (Must be full fat, not a reduced fat variety, my favourite being Philadelphia) 500g icing sugar.

Beat the butter till soft, add the cream cheese and beat briefly. Add the icing sugar and beat slowly until incorporated, then give a very quick blast with the beaters. Do not overbeat. The more you beat the softer it will become. Beat until you get it soft enough to pipe.
I use this recipe all the time to fill large cakes and also to pipe on to cupcakes. You can add flavour to it for example, vanilla seeds, orange or lemon zest, cinnamon etc

Sometimes this happens to me too but not always, and I always use the same recipe! I just came across this post on Nigella's site. This seems to be an adequate explanation as to why it happens and how to avoid it. http://www.nigella.com/kitchen-queries/view/Cream-Cheese-Icing-Turned-Runny/2531

Unfortunately occasionally cream cheese frosting does liquefy and this mainly comes from the liquid in the cream cheese mixing with the icing (confectioners') sugar and dissolving it, leading to a runny icing.
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We would suggest reducing/omitting the lemon juice as this adds extra liquid - you could use finely grated lemon zest instead if you want to add a lemon flavour
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There is a chance that the cream cheese was over beaten before the sugar was added [...] You could try making the frosting in a food processor, putting the sugar and cheese in together and whizzing for about 1 minute, until the ingredients are just combined.

We would also suggest using a recipe which contains part butter and part cream cheese. This is usually a bit more stable since the butter adds slightly more fat and is less likely to dissolve the sugar.

The way to do cream cheese frosting is to separately cream the butter and the cream cheese. Cream cheese tends to get runny if overmixed, while butter keeps on adding volume. So beat them separately and then combine. That way, you can arrange yourself on how "cheesy" you want your frosting to taste.

THE ONE FAILSAFE AND SIMPLE SOLUTION USING SAME RECIPE

I know this is an old thread but seems like no one has found the solution. I had the same problem for over 6 years, living in France and was very frustrated. Found this solution and I have no issues whatsoever now.

Beat butter and icing sugar together FIRST. You can add as much or as little sugar as you want to taste - this will not affect the result.

Beat the cream cheese in LAST. You cream cheese frosting will be delicious, not too sweet and totally pipe-able. You're welcome.

On the episode of Good Eats about Devil Food's cake, Alton Brown mentions that for cream cheese icing, the cream cheese must never have been frozen, which may result in the runny texture.

It's the proportions. I had a bad recipe as well and ended up with about 3 servings of the frosting when I was finished because of all the powdered sugar that had to be added. I eventually had to split the bowl and continue to add the sugar. My experience is for one 8 oz package of cream cheese, you need 1 stick of butter and about 3-4 cups of sugar and vanilla flavoring to taste.