After installing Xcode and I try to open it I get blocked with a message "Scanning for Plug-in failed" and that I may not have appropriate permission..I was logged-in as an administrator. Do I need "root" privileges?
If you are logged in to the admin account Xcode should open up without issues.
The only reason I can think of for this error would be that the plugin affected was corrupted or failed to install correctly.
You sould remove all xcode files, redownload it and start fresh.
Something to try if Graeme's answer doesn't work. Restart your computer from the recovery partition (if running Lion) or the gray disk (if not running Lion). Open Disk Utility and run a permissions repair on your startup volume. After this is complete, close Disk Utility and open Terminal from the Utilities menu. Type in
It's very important that you don't hold down the power button to exit the recovery session, or the ACL reset won't occur.
Let us know what happens.