The non-extended format sequential data set did not have an end-of-file record (EOF) where DFSMSdss expected one. Data sets with a track balance equal to a full track must have an EOF as the first record on the track pointed to by the last used block pointer. Data sets with a track balance less than a full track must have an EOF as the first record on the track following the track pointed to by the last used block pointer. This message be printed for data sets that have been allocated and never opened, as well as for data sets that have been opened, written to, and not properly closed (for example, the application or system terminated abnormally before the data set could be closed). This message also be printed if an I/O error occurs while trying to find the EOF.