You are sure that you do not have two tables with the same names. Yet you are still receiving this error message during export or import of data. One of the most common problems that will cause this error is that there are one or more tables without a name. From the design environment, if you see one or more tables without any names, this is the cause of the problem.
Provide a name for the table(s) and you will no longer see this error message and will not have any problems importing or exporting data.