Erro react-native run-android

Fiz a instalação do react-native-cli, android sdk e o emulador do android. Consegui fazer o init do projeto mas quando rodo o comando react-native run-android ele mostra o log:

Scanning 577 folders for symlinks in D:\dev\git-repo\cursos\reactNative\InstaluraMobile\node_modules (23ms)
JS server already running.
Building and installing the app on the device (cd android && gradlew.bat installDebug)...
Erro: Não foi possível localizar nem carregar a classe principal org.gradle.wrapper.GradleWrapperMain
Could not install the app on the device, read the error above for details.
Make sure you have an Android emulator running or a device connected and have
set up your Android development environment:
https://facebook.github.io/react-native/docs/android-setup.html