>I have a grid with 3 columns. the 3rd column is a checkbox. What I want is >that this checkbox appear disable for certain rows only. How can I do that?

Francisko,
You can use the checkbox's when event to determine whether to disable /control access to the checkbox.
Something like in the checkbox when event, you put:
RETURN lSomecondition

or

something like the following:
THIS.Enable=lSomecondition
THIS.REFRESH
RETURN lSomecondition
and lSomecondition return a logical value which determine whether access is allowed.

Kam.