After a bit of Googling I've found a way to do this.
The PC in question is 64bit and I had to enable the remote registry service, connect to the registry and make changes to allow me to connect to Radmin and to stop the users from locking me out again.
Here are the steps I took:
- Enable and start the remote registry service on the remote machine.
a) Open Command Prompt.
b) Type "sc \\computername config remoteregistry start= auto"
c) Type "sc \\computername start remoreregistry"
- Modify the remote machine's registry to switch off " Ask Remote User For Permission"
a) Connect to remote machine's registry (Regedit > File > Connect Network Registry and enter remore computer name.
b) Navigate to HKLM\Software\WOW6432Node\Radmin\v3.0\Server\Parameters and change the key AskUser to 00 00 00 00
- Modify the remote machine's registry to disallow user changes to Radmin's settings.
a) Create a new binary key in HKLM\Software\WOW6432Node\Radmin\v3.0\Server\Parameters called DisallowChanges with a key of 01 00 00 00
Of course, if the user is technically minded with admin rights they can simply delete the keys. However, I hope this is useful to someone.