If you receive a message like the one below.  Or one similar, this usually indicates, the CD drive or a netowrk drive is not accessible.

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Mirroring cannot be completed because of the error:

An unknown error occurred while accessing D:\lcr_20161109_082551.dcr.

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If this is a CD drive, remove the CD and try inserting a new CD.  If the message repeats, reboot the computer.

If this is a network location, contact your netowrk administrator to ask for access.