I don't know, what may cause the problem. If you can send me the data, I can try to experiment. Here is the code, which works for me:

oXtab = newobject("FastXtab", "FastXtab.prg")
oXtab.lCursorOnly = .t.
oXtab.lBrowseAfter = .f. && Don't show
oXtab.lTotalRows = .t.	 && Specifies whether to total rows in the cross tab output
oXtab.nTotalOption = 1   && Totaling options (0-sum, 1-count, 2-% of total).
oXtab.RunXtab()
if used('xTabQuery')

>I have set the lCursorOnly to .T., but still run into this error :"...Group by substatement is unvalid..."
>
>My prg is like this:
>______________________________________________________________
>oXtab = NewObject("FastXtab", "FastXtab.prg","", "tmpProj")
>oXtab.lCursorOnly = .T.
>oXtab.lBrowseAfter = .T.
>oXtab.RunXtab
>browse
>______________________________________________________________