You get this error when importing reports via the Import Reports feature in the Report Explorer:
Import file does not contain the DTools Report Definition File "ReportData.xml".
This is generally cause if you try to import an Excel Report or an "Order" Report via the Import->File feature in the Report Explorer:
These reports are not intended to be imported via this function. Only "standard" SIX Report archives (.dtr) and SI5.5 Report archives (.zip) are intended to imported via this function. For details on importing Excel or Order Reports, see Excel Reports and Import/Export Reports.