Steve ,

just to tell that this is such a dreadful problem :

i have run into the same problem , in a custom grid class , and tried to identify the cheeky little runt by adding a command button in my form that did something like

messagebox(type(form.grid.column.checkbox))

I got the same message that you did . It seems that it simply loads the object but doesn't init a value type . And i've tried setting that up in the grid.init and form.init events . I'm just going to read some more docs and debug a bit more and let you know if i find something out .