Ok, if the database looks fine then it must be something about the cookies. Authentication and roles are based on encrypted cookies that are set when you sign in.
Things I would try:
1. Sign out, clear your cookies and sign in again. Maybe even delete temporary internet files for good measure. Try different browsers, ie Firefox or Chrome, see if you get the same problem.
2. From another thread I know you have some other app running above or below mojoPortal. Consider whether your signing in to that app is a factor, perhaps it sets a cookie that overwrites or conflicts with the mojoportal cookies.
Hope that helps,
Joe