I cannot open Terminal at all because of this error message. (Probably the rudest error message I have ever seen on a computer.) This mac was originally a school computer and the permission to use Terminal was not given to me in the first place, so I have no clue about the method the "IT guys" used to keep me from using it, and therefore I do not know how to recover from it either. I have an admin account, though the account I usually use is standard, (I tried logging into other existent admin accounts presumably set up by the IT guys, but even in those accounts it was impossible to run Terminal), and I have already tried running permissions repair but it had no effect on the issue.
(p.s. I am not a very advanced user of mac, so descriptions fit for a newbie would be very much appreciated. Have seen a similar question on this website but it did not really help.)
Best Answer
Going by the appearance of the dialog window, it looks like the school you got this Mac from was using JAMF Software's Casper Suite to manage their Macs. One of Casper's features is being able to prevent specified applications from launching, with the additional option of providing a message to the end-user. As you're receiving this message, it appears that the Casper agent software is still installed on the Mac in question. There's an uninstall command to remove the Casper agent, but that would need to be run in Terminal. The article at https://jamfnation.jamfsoftware.com/article.html?id=153 by the authors of Casper explains how this is done.
At this point, I think the best bet is to back up your applications and data, wipe the drive of the Mac, and reinstall from scratch. It's the best way to make sure everything which the school had installed is now gone.