Sounds like another piece of software is trying to use it. Could be anything like Remote Assistance, Fax service, Windows Activation or Updates etc etc.
Try going in to Task Manager and stopping any service you think might be using it.
Or try this
If the telephone.ini file is missing or damaged, you can create a new one by running Tapiini.exe - this file is in the \windows\system folder. Before you run this, rename the telephone.ini file and reboot your PC if it already exists. Then, run the tapiini.exe file. This program will run very quickly and may not appear to do anything. You can verify the program created the telephone.ini file by searching for it.
The telephone.ini file is a Microsoft Windows file that stores settings for all TAPI-enabled applications including DUNS.