I solved the problem modifying manually the json file, but changing some values I don’t remember well, hehe.
My json looks now like this and it works fine:
{ "startColorAlpha" : 0, "startParticleSizeVariance" : 12.89041, "startColorGreen" : 0, "rotatePerSecond" : 360, "radialAcceleration" : 0.1, "yCoordFlipped" : -1, "emitterType" : 0, "blendFuncSource" : 1, "finishColorVarianceAlpha" : 0, "rotationEnd" : 0, "startColorVarianceBlue" : 0, "rotatePerSecondVariance" : 0, "particleLifespan" : 12, "minRadius" : 300, "configName" : "cloudsEquilibrium1", "tangentialAcceleration" : -0, "rotationStart" : 0, "startColorVarianceGreen" : 0, "speed" : 2, "minRadiusVariance" : 0, "finishColorVarianceBlue" : 0, "finishColorBlue" : 1, "finishColorGreen" : 1, "blendFuncDestination" : 771, "finishColorAlpha" : 0.5, "sourcePositionVariancex" : 1181, "startParticleSize" : 512, "sourcePositionVariancey" : 56, "startColorRed" : 0, "finishColorVarianceRed" : 0, "absolutePosition" : false, "textureFileName" : "cloudsEquilibrium1.png", "startColorVarianceAlpha" : 0, "maxParticles" : 90, "finishColorVarianceGreen" : 0, "finishParticleSize" : 512, "duration" : -1, "startColorVarianceRed" : 0, "finishColorRed" : 1, "gravityx" : -10.0, "maxRadiusVariance" : 0, "finishParticleSizeVariance" : 110.58, "gravityy" : 6, "rotationEndVariance" : -34.05, "startColorBlue" : 0, "rotationStartVariance" : 30, "speedVariance" : 14.13, "radialAccelVariance" : 5, "textureImageData" : "", "tangentialAccelVariance" : -0, "particleLifespanVariance" : 0, "angleVariance" : -0, "angle" : -180, "maxRadius" : 0 }