The CTI supports only one call at the moment.
However, when transferring existing calls to a third party, it can happen that some sessions are not correctly closed. You can compare that with a broken Lync conversation.
To solve this issue, right click on the CTI Toolbar icon and click on Drop calls and reset. Then try to make an outgoing call from the CTI Client.
If the problem still exists, try to completely shut down the CTI Client, shut down all left Lync / OCS conversations and open the CTI Client again. If the problem still exist, please contact the mscrm-addons support Team and send the appropriate log file to email@example.com.
Also, please check if the Lync Client and the MOC Client work correctly.
That's it! We appreciate your feedback! Please share your thoughts by sending an email to firstname.lastname@example.org.