frm-41316:Cannot set Insert allowed Property of disable item Line.Item_description

Dear All,

My Requiurement is On the Purchase Requisition  the description of the Item should not be change for Some of the User.

I Done the Following personlaization

Condition :

Trigger Event : When_New_Record_Instance

Trigger Object : Lines

Action :

Seq : 1

Type : Property

Language : All

Object Type : Item

Target Object : Lines.Item_Description

Property Name : Enabled

Value : False

When I Entering the Line the Item Description is Disable. But It is Giving the following message .

frm-41316:Cannot set Insert allowed Property of disable item Line.Item_description (Attachment)

Thanks and Regards

Afsar