Error with learn() when running example sb3_4x4grid.py

[sigmarco3]

Hi, i'm running the example sb3_4x4grid.py but when the metod learn() starts i get this error :

looking at the file where the program stops, which is "vecEnv.py" it seems that it calls an abstract method and that it should return 4 variables, but it doesn't as the error in the picture says. Has anyone else had the same problem? My stable_baselines3 version is 2.0.0a0