I'm not positive, but I think that you need to reformulate your field equation. Try ...
SetFieldByName( “TableName::” & $FieldName & "[" & $Repeat & "]" ; Value= $Value)
If that doesn't work, try enclosing the whole thing in the Evaluate function.
(p.s. there are one too many close-parentheses in your equation, as shown)
That did it, thanks. Should have thought of that...