| Class | TranslationUnavailable | Translation objects are unavailable. |
| Class | NotFoundError | Launchpad object not found. |
| Class | GoneError | Launchpad object is gone. |
| Class | NameLookupFailed | Raised when a lookup by name fails. |
| Class | UnexpectedFormData | Got form data that is not what is expected by a form handler. |
| Class | POSTToNonCanonicalURL | Got a POST to an incorrect URL. |
| Class | UserCannotUnsubscribePerson | User does not have permission to unsubscribe person or team. |
| Class | SubscriptionPrivacyViolation | The subscription would violate privacy policies. |
| Class | ServiceUsageForbidden | The specified ServiceUsage is not allowed. |
| Class | IncompatibleArguments | Raised when incompatible arguments are passed to a method. |