iTunes says my password is incorrect for certain apps

I have tried at least 20 times and this has been going on since yesterday! I can use my iTunes account perfectly to download most things, but there is an app that I need to update (it's one of those apps that if you don't update it what an update is available, it crashed like crazy) but when I try to update it, the "Apple ID or password is incorrect" notification pops up. And it's not like it's a typo! I have tried 20 times. I have slowly typed my password, one letter at a time, I even tried my OLD password one time. I have tried over again at least 20 times. It's SO FRUSTRATING. Has anybody had this problem before? How did you fix it? Thanks 🙂