If you upgrade an ESM manager to version 9.0 from any of the previous versions, Symantec ESM resets the existing licenses on that manager to 0 (zero). You need to assign fresh enterprise licenses on the ESM console and assign them to the managers.
You can operate with 6.x licenses if you have an ESM console 9.0 with managers with versions earlier than 9.0. However, the new Enterprise licenses replace the old licenses if you distribute new licenses to the managers using the console.
The existing licenses on the ESM managers with a version earlier than 9.0 are not compatible with ESM 9.0 managers. You must get these old licenses converted to enterprise licenses by contacting the Symantec Licensing Administrator at firstname.lastname@example.org