Fix DistBackendError

✅ Solution

DistBackendError usually occurs when the distributed training environment isn't properly initialized, often due to NCCL issues or incorrect configuration of `torch.distributed`. Ensure NCCL is correctly installed and configured by verifying `NCCL_DEBUG=INFO` environment variable output; then, double-check your `torch.distributed` initialization script (e.g., `torch.distributed.init_process_group`) for correct `backend`, `rank`, and `world_size` values. Using the correct device (GPU) can also resolve the error.