A ledge or cliff in a dream can refer to something in waking life that is on the verge of going in the wrong direction.
If you are trying to cross a ledge, then it is most likely connected to a temporary but difficult struggle you may be dealing with in waking life. The level of difficulty you have in the dream is connected to how difficult this current situation is for you to get through. The message is to hang in there, don’t give up. Be firm in your beliefs, just as you would need to have firm footing on the ledge, and know that you’ll get through it soon enough.