I am building a grid with variable number of columns.
Need to set the control source for each column when the form starts up.
In the form Init I have the following two lines that work:

THISFORM.PageFrame1.Page1.Grid1.COLUMNS(I).Header1.CAPTION = PROPER(EmpCaption)

THIS.PageFrame1.Page1.Grid1.COLUMN2.CONTROLSOURCE = "RIGHT(ApptC.Emp1, 25)"

But this does not:

THIS.PageFrame1.Page1.Grid1.COLUMN(I).CONTROLSOURCE = RIGHT(CSstring, 25)

I get an error "COLUMNS(I) is not an object"

Why does that not work and or how to use COLUMNS(I) to set the control source?