How did you install caffe2 and PyTorch in the past?
It should be possible to install both using conda.
Currently some old lib seems to bug the import.
Also, as far as I know, caffe2 is already included in the current PyTorch binaries.
Could you just install the latest PyTorch release and try to import caffe2?
If that yields the same error, try to uninstall old caffe2 builds.