DaleOnyon, two suggestions:
1. Do not downgrade from Admin to common user and, on contrary, upgrade. This could mess access permition to programs and your Windows. I have trouble in the past. Maybe I've done something wrong but just a friend suggestion.
2. Do not use more than one account with Admin privileges (same reasons).
But, about your 'problem', avast works fine with one Admin account and others common. No problems at all.