Hi ,
n
You don't need to set the Auto Post Back attribute on the Task Complete field at all–uncheck Auto Post Back. Just create a Form Component behavior on the Comments field and go to the required when section. Make the Comments field required when the "Task Complete" is equal to "Yes" and then enter a message when the requirement is not met. Do this for the New Form and the Edit form. Here is what my XML in qListForm looks like which worked fine for me:
n
<FormComponentBehavior>
<Component Type="Field" ID="Comments">
<RequiredWhen Message="You must provide a Comment when the task complete is Yes">
<Eq>
<FieldRef Name="Task_x0020_Complete" />
<Value Type="Choice">Yes</Value>
</Eq>
</RequiredWhen>
</Component>
</FormComponentBehavior>