This category indicates that the request could not be delivered to the intended receiver, because of a path outage, a sequence of activation requests that is not valid, or one of the listed path information unit (PIU) errors. Some PIU errors fall into other categories; for example, sequence number errors are sense code category X'20'. A path error received while the session is active generally indicates that the path to the session partner has been lost.
Category and modifier (in hexadecimal):