Shizzam shizzam have I got a solition for you.
First shut down the mac. Once its off hold down the command and R keys.
Press the power button like you normally do and continue to hold command R for a moment
this will put it into recovery mode and give you a list of languages, hit the right arrow at the botttom
on the next screen ignore the OSX utilities and look at the top bar of the screen
click on "Utilities" on the top bar, not "OSX Utilities"
then click on terminal
this opens a black box, you are now using UNIX, be sure to brag to your friends at the office watercooler
type: resetpassword with no space between the 2 words then press return
this opens the password reset utility. Click on the "MacintoshHD" at the top, or whatever you may have renamed it. On the next line click on the account name and change it to "Administrator ROOT"
Root = GOD btw
enter a password twice and hit save
for the love of fishsticks do not hit "reset" at the very botton, it won't fix anything for you
you will get a message that it was succesfully reset, hit ok
next hit the apple at the top left corner of the screen and select restart
now login to the mac, note that Root will not be listed
once logged into one of the managed, non admin, accounts go to system preferances - users and groups
click on the lock icon at the borrom left of the window and a password box will open
use: root in all lower case with the password you just set.
BAM! you can now change your restricted accounts back to Administrative.
I had huge trouble from corruption in Lion, 12 serious glitches lasting for 9 months. The Apple Centre thought that there was corruption in my User Account (I had installed Lion, and re-installed it, by not using an erase and install method). I erased and installed M. Lion and have had mimimal trouble since. I prefer the erase and install method despite it being more trouble in re-setting things.