hi i am new to ubuntu and ros and i had this error when launching Gazebo,

Msg Connected to gazebo master @ http://localhost:11345 Error [Transport.cc:102] Unable to get topic namespaces in [50] tries. Error [Node.cc:68] No namespace found X Error of failed request: BadRequest (invalid request code or no such operation) Major opcode of failed request: 154 (GLX) Minor opcode of failed request: 19 (XGLXQueryServerString) Serial number of failed request: 12 Current serial number in output stream: 12 ^C[gazebogui-3] killing on exit [emptyworldserver-2] killing on exit [gazebogui-3] escalating to SIGTERM [emptyworld_server-2] escalating to SIGTERM

not sure what's wrong or how to fix it, please help..