Traincar asset must have at least two bogeys.
KIND Traincar assets are required to specify a minimum of two bogey attachment points (specifically: "a.bog0" and "a.bog1"). This validation error results when one or both bogeys are missing.
This validation results in an error at trainz-build 4.5 and higher. In lower trainz-build assets, the validation is considered a warning for compatibility reasons, however it is likely to lead to undesirable runtime behaviour.