I'm quite new to my IT role within this company, and I'm doing an upgrade to AutoCAD 2014, if I install simulate as well then the it will try and install Simulate again when the users are doing various things like PDF plotting and accessing other programs. They don't have the permissions to install on their user accounts, but I'm wondering why this is even happening? And how I can fix this?
Any help would be greatly appreciated
Welcome to the community.
If you are using roaming profiles, or redirecting user profile folders (i.e. My Documents) to another location or network drive, then this could be part of the problem.
To resolve this issue, you probably need to move the profile back to the local default location and let the installation complete, then move it back. That typically works.
On a soap box note, as a network administrator myself I recommend that you should also give your engineers local admin rights to their machines to prevent behavior issues like this. Having local admin rights on a workstation does not yield any additional privileges on the domain and you can still illicit company policy restrictions via your GPO. There's no reason to handicap your engineers. Doing so only causes the problems that you are enquiring about.
Good Luck!