Problems with AT&T Calling Card

Setting up an AT&T Calling Card on a laptop with Windows 98SE with the correct pauses between the numbers and the call disconnects after the destination number is dialed, but before completion of the call. Internet, Dialing, and Modem Properties have all been checked for any discrepancies, particularly the Connection Tab of the Modem Properties, i.e. Call Preferences. The modem driver was updated. Direct dial-up to the destination number works fine. Why is the call disconnecting?