File "C:\Panda3D-1.11.0\direct\task\Task.py", line 534, in run
    self.step()
  File "C:\Panda3D-1.11.0\direct\task\Task.py", line 488, in step
    self.mgr.poll()
  File "C:\Panda3D-1.11.0\direct\showbase\ShowBase.py", line 2019, in __igLoop
    self.graphicsEngine.renderFrame()
AssertionError: _total_size == 0 && _count == 0 at line 30 of c:\build\panda3d-exe\panda\src\gobj\bufferContextChain.I