In your softphone user configuration, be sure to have enable CTI application use checked. Also, your CTI port has to be configured with the name of the PC exactly as it appears. Be sure to associate your softphone user with the CTI Port. Finally, make sure your username/passwords are sync'd up on the TAPI driver on the PC (control panel--phone/modem--advanced) and in the CM user.
If you upgraded CM lately, you may need to upgrade your softphone/TAPI as well.