Check the call-waiting setting
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  1. In the dialing error screen, click Dialing Properties.

  2. If your telephone system has call waiting, it should be turned off while you are dialing from your computer. You can turn it off by clicking the appropriate value for your telephone system in the To disable call waiting, dial list.

    For example, on many phone systems you click *70 to turn off call waiting. If you are not sure which value to use, contact your telephone company or your phone system administrator.

  3. Click OK, and then click Next.

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