Standing at a locker and not remembering the code is read as being cut off from something you need right when you need it. It often returns from school days as a picture of pressure and small public panic.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.