The problem was resolved as follows:
We first checked the fiscal periods via the Fiscal/Financial Periods Setup window within Dynamics itself – and reviewed the periods for all the years back to the beginning in 2003.
They all looked fine.
However then we ran the SQL Script to check this same information in the SY40100 table, as follows:
select PERIODID, PERNAME, YEAR1, PERIODDT, PERDENDT from SY40100 where SERIES=0 and PERIODID>0 order by PERIODDT
The results of this script reported problems – over laps with period and invalid end dates in the 2003 year which impacted 2004 also.
We then corrected these problems – as per KB below:
871789 How to re-create fiscal periods in Microsoft Dynamics GP
https://mbs.microsoft.com/knowledgebase/KBDisplay.aspx?scid=kb;EN-US;871789
The Data Provider Framework problem then no longer occurred - and we were able to create report definitions and run reports ok on the particular Dynamics company.
So the lesson learned here, is that the view of the fiscal period setup data in Dynamics itself may in fact be misleading – and the SY40100 table in SQL is the true view of the state of play.