| Code | Description |
| 421 | Service not available. |
| 450 | Requested action not taken (e.g., lock already in use). |
| 451 | Requested action aborted (e.g., local error in processing). |
| 454 | Temporary authentication failure. |
| 500 | General syntax error (e.g., poorly-formed XML). |
| 501 | Syntax error in parameters (e.g., non-valid XML). |
| 504 | Parameter not implemented. |
| 530 | Authentication required. |
| 534 | Authentication mechanism insufficient (e.g., too weak, sequence exhausted, etc.). |
| 535 | Authentication failure. |
| 537 | Action not authorized for user. |
| 538 | Authentication mechanism requires encryption. |
| 550 | Requested action not taken (e.g., no requested profiles are acceptable). |
| 553 | Parameter invalid. |
| 554 | Transaction failed (e.g., policy violation). |
| 555 | Extension (ProcessInfo) used not supported. |
| 556 | Required extension (ProcessInfo) not present. |
| 557 | StaleCredential (A bad LastModified value was contained in an UploadRequest.). |
