Q: Verification failed - App store

For the past few weeks, I've been experiencing login errors from the App Store ranging from "verification failed" to "connection failed" on my iphone 5. Though the main problem is my "apple ID/password being incorrect" although both of my ID and password works fine logging in apple.com and itunes. I've tried logging in a hundred times and changing my password yet this error keeps popping up on me. I've tried logging in another apple ID of mine and it worked fine but my main ID seriously won't let me log on. My ID works everywhere but the iphone app store which doesn't make sense. Please help I urgently need to update my apps.