Unable to make changes through Admin User

I am unable to make administrative changes while logged into my Admin Account (the only account on my iMac 3.4Ghz intel core i7).

I first noiticed the problem when I attemped to copy a plugin I had just downloaded (from a reliable developer) into the plugins folder for the Software I intened to use it with. I was asked to enter my U/P, after entering I received the error message "The Operation cannot be completed because an unexpected error occured. (Error Code 100022)."

The error persisted when I tried update my adobe software, I entered my u/p and was then informed that "Administrator privileges are required to apply update to your product."

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Things I've tried:

I first tried to change privelages to the Plugins Folder in the Info Panel by unlocking the lock a the bottom. I am prompted for my admin u/p. I enter it correctly. press enter. It accepts the u/p but the lock stays in the locked position.

In System Prefs/Users I've attempted to add a new admin, by unlocking the lock at the bottom, and entering my password correctly only to have the lock remain locked.

Through Disk Utility I verified and repaired permission with no change in behavior.

I've restarted in Recovery Mode (Restart, Command + R ) and attemped to repair the permissions. No Change.

Restart in Safe Mode ( Restart while hodling down shift), which brought me to a login screen with my admin user, and guest user, but wasn't allowed to login using my Admin U/P.

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I'm at the end of my rope here. About to back up what I can and wipe the thing and try again.

Suggestions?
Thanks.