The following error response codes may be returned by calls to the server or client Constituent API (CRConsAPI or SRConsAPI).
| Code | Description |
| 10 | One or more required constituent fields are missing. |
| 11 | Add failed: duplicate. |
| 12 | Update failed: duplicate user name. |
| 13 | Update failed: duplicate e-mail address. |
| 14 | Method not allowed. |
| 15 | Update failed: matched multiple records. |
| 16 | Constituent record not found. |
| 17 | (Deprecated) No method was specified. |
| 18 | Attempt to access a user field did not match any records. |
| 19 | Error returning group membership. |
| 20 | Invalid password. |
| 21 | Change password error: the old password is required. |
| 22 | Validation error. |
| 23 | Input size error. |
| 24 | Address correction service error. |
| 25 | Invalid date range. |
| 26 | Invalid interaction type. The specified interaction type ID does not refer to a type of interaction that can be added with this API. |
| 27 | Invalid interaction. |
| 28 | Interaction logging failed. |
| 29 | Invalid cateogry ID. |
| 30 | Interaction body too large. |
| 31 | Maximum number of interactions exceeded. A limited number of interactions may be specified in each invocation of this method. |
| 32 | Invalid constituent ID for interactions. |
| 33 | No fields are configured to support authentication. |
| 34 | UK Address Lookup Error. |
| 35 | Input contains invalid characters. |
| 36 | Usernames that are email addresses are not checked. |