Alexa Skill Builder | A sample utterance is invalid

Playing around with the Skill Builder for Amazon Alexa the following problem occured while building the model:

A sample utterance for a slot in the interaction model is invalid

I tried a few things to solve the problem but i could not find its source. It was not coused by the custom slots itself, because when i removed the utterances from the intents the models was building fine.So the problem was in direct correlation with the utterances themself. Here is a little sample utterance from my model definition:

...

      "samples": [

        "Add {object}.",

        "Append {object}."

      ],

...

The solution to get the build running

After some time i came around this Amazon Developer Forums thread  which pointed into the right direction. The curly braces must be isolated from any other character. It is not possible to write a non space symbol next to the first or last curly brace. So if you get stuck with this problem this may be your solution.