I thought I had found it, I was not reordering the fields in the report correctly. But I still get the error. It looks as though I am somehow corrupting the .frt file. Here is the basic process I am following.

1. copy the existing report to a temp frx (and frt)
2. add the report objects:

APPEND BLANK
REPLACE PLATFORM WITH "WINDOWS", UNIQUEID WITH SYS(2015), NAME WITH "DTEXT", ;
OBJTYPE WITH 8, VPOS WITH 14166.667, HPOS WITH 2500, HEIGHT WITH 1770.833, ;
WIDTH WITH 5104.167, FILLCHAR WITH "C", FILLRED WITH -1, FILLBLUE WITH -1, ;
FILLGREEN WITH -1, FONTFACE WITH "Times New Roman", FONTSTYLE WITH lnFontStyle, ;
FONTSIZE WITH 10, MODE WITH 1, FLOAT WITH .T., NOREPEAT WITH .T., OFFSET WITH lnOffSet, ;
RESETTOTAL WITH 1, SUPALWAYS WITH .T., SUPEXPR WITH lcSupExpr

3. reorder the reports

SELECT * FROM (lcReport) WHERE OBJTYPE < 8 INTO CURSOR CUR1
SELECT * FROM (lcReport) WHERE OBJTYPE = 9 INTO CURSOR CUR2
SELECT * FROM (lcReport) WHERE OBJTYPE = 8 INTO CURSOR CUR3
SELECT * FROM (lcReport) WHERE OBJTYPE > 9 INTO CURSOR CUR4
SELECT (lcReport)
DELETE ALL
APPEND FROM DBF("CUR1")
APPEND FROM DBF("CUR2")
APPEND FROM DBF("CUR3")
APPEND FROM DBF("CUR4")

I have checked the memo with FoxFix, but everything is reported OK