Cannot spawnModel from MATLAB

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I want to do connection between MATLAB and Gazebo and generate Gazebo model from MATLAB. I follow the instruction in add-build-and-remove-objects-in-gazebo, and the following commands work successfully.

rosinit(ipaddress)
gazebo = ExampleHelperGazeboCommunicator;
ball = ExampleHelperGazeboModel('Ball') 
spherelink = addLink(ball,'sphere',1,'color',[0 0 1 1])

But when I run the next command spawnModel(gazebo,ball,[8.5,0,1]), the errors show up in MATLAB command window:

Error using ExampleHelperGazeboCommunicator/startModelServices (line 334)
Failed to create a /gazebo/get_model_state service client.

Error in ExampleHelperGazeboCommunicator/spawnModel (line 290)
            startModelServices(obj);

[ERROR] ServiceClientHandshakeHandler - Service client handshake failed: client wants service 
/gazebo/get_model_state to have md5sum af0f702011820738976b120226dc9d96, but it has 
4c515e936d3319c9610c559c60bfc3d4. Dropping connection.

The error shown in ubuntu terminal is

[ERROR] ServiceClientHandshakeHandler - Service client handshake failed: client wants service 
/gazebo/get_model_state to have md5sum af0f702011820738976b120226dc9d96, but it has 
4c515e936d3319c9610c559c60bfc3d4. Dropping connection.

I use matlab 2018b, Robotics System Toolbox2.1 on win10, and Ubuntu18.04, ROS melodic, gazebo9 in virtualbox, which are all newest version. Does anyone know how to solve it?