Re-activating InstallShield 2010 Flexera Software Failed

I need to re-activate InstallShield 2010 – Flexera Software since users are required to re-activate the software every year.
The automatic re-activation failed so I have to manually re-activate it but received an error stating that the license is already in use. How can I re-activate it?
Please help me.

The license for this computer is in use on another computer.
Please return the license from that computer to use it on this computer. You may return a license using the Help|About menu option, or uninstall the product from the other computer. You may also opt to purchase a new license.
Error 20653 – The number of activations allowed for this account has been exceeded.
Purchased a New License
