There are little tweaks to the structure of a journal between releases. Journals are generally forward-compatible without issue, but you'll get that error going backward through releases. The good news is that I haven't run into any actual differences that impact functionality. Just click okay, and save the journal. The error shouldn't show up again.
That said - you probably should just upgrade to JMP 15 (you're two releases behind now). Most likely, your license allows for access to the latest update, you just have to ask your license admin. If you need help figuring out who that person is, just drop a note to tech support (support@jmp.com) and they should be able to help.
M