I got problem with join one to many show single row

[dutch]

When I use GROUP BY to group the row. It has got an error

Warning BASE/39 Write not allowed: FWMARIAROWSET:tbl_rmno

If I do not use GROUP BY, it has no error. But it will show multi rows.

I guess, GROUP BY will not allow to edit.

Error occurred at : 04/10/18, 23:28:19
Description : Warning BASE/39 Write not allowed: FWMARIAROWSET:tbl_status
Args:
[ 1] = C R

Stack Calls
==========================
Called from : source\rtl\tobject.prg => FWMARIAROWSET:ERROR(0)
Called from : .\source\internal\FWMARIA.PRG => FWMARIAROWSET:FIELDPUT(2294)
Called from : .\source\internal\FWROWSET.PRG => FWMARIAROWSET:_TBL_STATUS(1243)
Called from : D:\V6\EZ4FO\EZRSVN1.PRG => DUPRSVN(4804)

How Can I fix it?

Thanks in advance.