admin account gets downgraded to limited user account

hello every one
I was hoping if some one could help me at this.
I had created a local account in my machine which is a part of a small office network. and given it administrative rights. every once in a while the account gets downgraded to a limited user account and a I had to go all the way to control panel to reset the settings for that specific user account. I tried background check on the machine to check it for possible malware or virus infection but couldn't find anything.
could it be the user profile settings getting changed athomatically due several usages or could it be log file getting full or needs to be cleared?
so much in need for help

possibly because that comp didnt come with Ultimate and when it re-activates, it uses the true Admin account and resets the others.

Roy