Access SQL UPDATE with a correlated sub query on a single table

Question

I have a table with a grid reference string, a year number and a total number (HectadGridRef, YYYY and TotalRecordsAllSpecies). I have added a column, FiveYearTotalRecords. I want to update the new column with values from adjacent years (two years before and after) so that with further processing, I can handle a five year rolling window.

I have tried this on a test version of the table:

UPDATE tblYRAllSp5yeartest01 AS XX  
 SET FiveYearTotalRecords = (SELECT SUM (ZZ.TotalRecordsAllSpecies) FROM tblYRAllSp5yeartest01 AS ZZ  
 WHERE (ZZ.HectadGridRef = XX.HectadGridRef)  
   AND (ZZ.YYYY > (XX.YYYY - 3))  
   AND (ZZ.YYYY < (XX.YYYY + 3))); 

but I get the message "Operation must use an updateable query".

I suspect that the problem is that I am trying to update a table that is already open (by the sub query). Is that the case? Is there any way around it other than making a copy of the table and pointing the sub query at that instead?

[Edit: I have tried it with a copy of the table and I still get the same message, so I can't think where the problem is. As far as I can see, I have appropriate permissions to the whole database].