Why have I lost my second ZBrush activation?

Under the previous Pixologic licensing system, a single ZBrush license could be activated on multiple machines. This was intended to allow one user to move between systems, such as a home computer and a work computer, but it was not permitted for concurrent use. Only one active use at a time was allowed under the license agreement.

Under the current MyMaxon licensing system, ZBrush can be installed on as many machines as needed. The license itself is assigned through your Maxon account and can be activated on the machine you wish to use.

If you need to move your license to a different computer, you can manage activations directly through your Maxon account portal.

For detailed instructions, please refer to:
 How do I use my license on a different computer?