The error doesnt show up for me. I think your Half-Life files are corrupted or something like that since some entities dont show up in your grid. Try reinstalling Half-Life, if you installed any addons try to uninstall them first. If you dont want to reinstall Half-Life, go to your Half-Life folder, delete the models direcetory, and in the Steam library right click on Half-Life, Properties, Local Files, Verify file integrity.
It should work