小中大1. The protein might not be abundant.
2. Santa Cruz always recommends to use their primary antibody from 1:100-1:1000 for western blot, is that right? Can you double check your datasheet of the antibody?
3. The antibody might not be good. Sometimes it happens. Call, describe your problem, ask them to send new batch of antibody, or change another antibody to the same protein(eg. C-20--> H300), they have good custom service.