your error message sounds like you forgot to give out a User Access Token to that login credentials. So you say that the actual "master"-account that has set up all this is working on ipad? That really sounds like my idea. How to set up User Access Tokens, you can see here.
Hope i could help you.
Without having much background here, I suspect you're running into a known issue. With iOS / Mac devices, if you have Windows authentication set, then the user will be rolled over to form login. Due to a known bug when using form login, the user needs to have the local security setting to be able to login locally (Allow login locally) set. Add that user(s) to have that right and report back.