compiler fails converting compelled general type

i have category general form "g"

in category denote i have

public category detailelement : elementdefinition

let's contend i have slight this

        open vacant dosomething<g>(g generic)
            where g : elementdefinition
        {
            (generic detailelement)
            {
                ((detailelement)generic).descen = "hello people"; //line 1
                //////
                elementdefinition component = generic;
                ((detailelement)element).descen = "hello again"; //line 3
                //////
                (generic detailelement).descen = "howdy"; //line 5
            }
            else
            {
                //do stuff
            }
        }

compiler reports blunder line 1:

cannot modify form 'g' 'detailelement'

but line 3 works fine.
i workaround emanate doing formula combined line 5.

what i know since does compiler reports blunder line 1 line 3, given that, distant i know, identical.

edit: i am fearful i competence blank vicious square horizon logic

edit2: nonetheless solutions compiler blunder important, doubt since compiler reports an blunder line 1 line 3.