One possibility is that you are assigning the role in the wrong context. Moodle has a slightly complex context system that gives a lot of flexibility but can be confusing. Here's the moodle documentation on it:

http://docs.moodle.org/19/en/Context

To give admin access you need to assign the role in the system context, whereas you may be assigning the course creator role in a course context (via Assign Roles on the course page).

Can you confirm that you are assigning the administrator role like this:

Click Site Admin > Users > Permissions > Assign System Roles

Click 'Administator', then select users to add.

If that's what you did, the other thing to check is that the administrator role has the right capabilities:

Click Site Admin > Users > Permisions > Define Roles

Click the edit button next to 'Administrator'

Make sure the appropriate capabilities are set to 'Allow' and save.

Simon