If you have upgraded the operating system from lets say V5R4 to V7.1 you cannot save your data back to V5R4 level. On your save commands it will only allow you to go back one release level. Therefore from V7.1 you can only save back to V6.1. On the save commands (e.g. SAVOBJ, SAVLIB) you can specify the oldest level of the operating system you want to save to. This also applies to compiling your programs where you can only go back one release level.