Hi Hakim,
Rebecca is correct.
You cannot place a 10.2 Concurrent Use license onto a 10.0 License Manager. The License Manager must be the same version (or higher) as the license type you wish to authorize.
Also, the License Manager must the same version (or higher) as the clinet machine trying to connect to it, i.e. a 10.2 client cannot connect to a 10.0 License Manager, but a 10.0 client can connect to a 10.2 License Manager.
My recommendation would be to always run the latest version of the License Manager, and ensure that the license are upgraded to match it. This way, all client machines will be able to connect to it, regardless of what version they are on.