Grant Permission on a item for a user

Sep 9, 2008 at 6:01 AM
In my Workflow, I want to grant "Edit" right to Created By to change value of a item's field.
because i think workflow have the same role with Created By who init this workflow.

I have set two activities sequently as below:
1. Grant "Contribute" Role for Created By.
2. Set Status to value: "Approved".

But Exception throw: Access denied.

Who can help me?

thanks in advance,