HI Ivan Pazmino,
the validation error that you get is related to the simulation feature. And it should not prevent you from building the package in guvnor.
If you do want to get rid of that validation error,
Look at my attachment ("gate probability.png")
basically, if you have gateway like that, then you need to ensure that the probability sum of the two out flow is 100, so in my attached diagram you can give 50 for both probability value of out flow and that should get rid of that validation error.
But once again, it is optional to do this.
gate probability.png 33.4 KB