Security in a form

Hi,

I am facing an issue in setting security for a form

my Problem is: all values on the form should be "read only", but one control on the it should be able to edit.

E.g., the employee become a "read only role" for the form, but needs also a "edit role" for a special fields on the form

Is there any way for this.

I set the Needed Permission to Manual in the form for the special fields. and Mapped them to Read in Permission node of the form

Also tried setting the access for these fields in privileges too.

But did not give the expected result.

I am able to click the edit button in the form but all the fields are not editable including the special fields.

Else it would be other way - on Clikcing edit button, all the fields are editable.

Could you please help me on this