Visual Assist is licensed per developer, not per PC. If an activation key is installed to Visual Studio in one Windows user account on a PC, the activation key may not be installed to, or used by, another Windows user account on the PC unless its user also has a license for Visual Assist.
If an individual no longer needs Visual Assist on a PC, uninstall Visual Assist from his Windows user account. By default, his activation key remains in the registry should the licensed individual need, in the future, to again run Visual Assist on the PC.
To prevent a different individual from installing and using the activation key for Visual Assist in the Windows user account of the licensed user, assuming another individual can gain access to the user account, deactivate the account entirely by deleting the following entries from the registry of the account:
HKCU\Software\Whole Tomato\Visual Assist X\UserName
HKCU\Software\Whole Tomato\Visual Assist X\UserKey
If Visual Assist was installed using instructions for automated installation, delete also the following:
HKLM\Software\Whole Tomato\Visual Assist X\UserName
HKLM\Software\Whole Tomato\Visual Assist X\UserKey