Hi SDAC
Welcome to the Community Forum, I hope you find it a valuable resource.
We are aware that with the Purchase Register Detail report, if there is any purchase order has a layout type as Professional or Miscellaneous during the reporting period, it would cause the error. This is still something our developers are investigating, in the meantime, please change the purchase order's layout to Service or Item.
A quick way to locate the offending transaction would be using the Import/export assistant, set the layout, status and date period and export the list.
I hope this helps. If you have any other questions please feel free to let us know.