The problem occurs because the TMCM service account is using a different account instead of the local system. Change the account to the local system account and restart the services to fix the issue:
- Go to Services of the Microsoft Management Console (MMC).
- Double-click the TMCM service from the list.
- Select Log On > Local System account > OK from the pop-up window.
- Manually restart the TM service by going back to Services, right-click the TMCM service and select Restart.
- Log on to TMCM and click Administration > Account Management > User Account and the Import AD users option should appear.