[Closed] SetOffset in a script controller

I need to control the V_Offset of dozens of maps with one custom attribute spinner.
I am writing a Maxscript to automatically set up a float script for each V_Offset parameter.

So far if I animate the spinner and scrub the timeline the V_Offsets update correctly but I would like to add a time offset to the float scripts too.

ctrl = float_script ()
 meditMaterials[24].materialList[1].Color_map.Maps_0.Coordinates.V_Offset.controller = ctrl
 --This puts a float script onto the V_Offset parameter of the correct map
 
 ctrl.Addtarget "driver" $MasterObj[4]
 ctrl.SetOffset " driver " 10
 ctrl.setExpression "driver.CustAtt_A"

Currently this script sets up control but without any time offset even though in the Script controller dialogue the tick offset is set to 1920 (10 frames).

I think the problem stems from the addtarget line:

ctrl.Addtarget "driver" $MasterObj[4]

I tried the following but it doesn’t help:

ctrl.Addtarget "driver" $Text002.baseobject.custom_attributes

Also tried this too but it creates an error:

ctrl.Addtarget "driver" $Text002.baseobject.custom_attributes.CustAtt_A
 -- Runtime error: IScriptCtrl::AddTarget - Target needs to be object or subAnim, got: -0.0200213

Thanks for any help!
Graham