My Turbocad V18 has developed an issue (probably something I have done/not done) in that when I launch it and try to open an existing drawing, the programme home screen is all greyed out and nothing happens.
There was a time in the past (can't remember when) where a dialog box would be behind the TC window, I think this was usually the start dialog though, this prevented TC from being used until the dialog closed via the taskbar, this only works if the dialog is a separate window as in the case of the start menu.
There was also a report recently of a dialog being 'off screen' which again prevented TC from being used, the problem occurred after changing from two monitors to one monitor, if the File Open dialog was 'off screen' it would prevent TC from being used, and this can't be corrected via the task manager, but has to be corrected manually.
Don't know if any of the above rings a bell with your situation.
With regards the permission, I agree with MachGTX, it sounds like your saving a file to a restricted place, some things like Templates are stored in a place that some Windows installation will not allow file to be saved there by a program (can be done manually though), this is usually a Windows restriction, check the file path when you are trying to save the file.