> ## Documentation Index
> Fetch the complete documentation index at: https://docs.coreweave.com/llms.txt
> Use this file to discover all available pages before exploring further.

# What do common sandbox SDK error messages mean?

The following table summarizes the most common exceptions that the SDK raises, along with their typical causes and recommended fixes.

| Error | Cause | Solution |
| - | - | - |
| `CWSandboxAuthenticationError` | Missing or invalid credentials | Check the credential for your selected [authentication method](/support/sandboxes/articles/why-does-the-sandbox-sdk-raise-an-authentication-error) |
| `SandboxNotRunningError` | Operation on stopped sandbox | Check `sandbox.status` before operations |
| `SandboxTimeoutError` | Operation exceeded timeout | Increase `timeout_seconds` or optimize command |
| `SandboxTerminatedError` | Sandbox ended externally | Check `max_lifetime_seconds` or external termination |
| `SandboxFailedError` | Sandbox failed to start | Check container image and resources |
| `SandboxNotFoundError` | Sandbox deleted or never existed | Verify sandbox ID is correct |
| `SandboxExecutionError` | Command returned non-zero (with `check=True`) | Check `e.exec_result.stderr` for details |
| `SandboxFileError` | File operation failed | Check file path and permissions |
| `FunctionSerializationError` | Can't serialize function args | Use JSON-serializable types or `Serialization.PICKLE` |
| `AsyncFunctionError` | Async function passed to `@session.function()` | Use sync functions only |

<Badge stroke shape="pill" color="blue" size="md">[Server Errors](/support/sandboxes/tags/server-errors)</Badge>