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Can the 411 Directory be reached? Does the caller hear a prompt for the letters of the name? If not, try dialing 411 directly from an internal extension and see if it prompts for the letters of the name. If not, you may want to delete the 411 extension and set it up again. If it can only be reached internally and not through an incoming IVR, then check the Incoming Call Route and the IVR menu to be sure that it is setup correctly.
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If you have checked all the above and there still seems to be a problem with the Dial by Name from an IVR, you should run a packet capture while attempting to call into the server and use the Dial By Name Directory. Ask Technical Support to review the packet capture for problems. SeeHow to Run a Packet Capture