scroll box automatically

i have used GUI.BeginScrollView , EndScrollIView and ScrollTo to scroll a box vertically .it work properly, after finishes its scrolling i positioned the y value in ScrollTo function to 0...then i can't scroll the box as normal using mouse ......help me

here my coding

if(teach_cam.camera.enabled == true) { twalkmesh1.active = false;

    if(table == 0)
    {

        GUI.skin = uin;

        spos = GUI.BeginScrollView (Rect (0,0,Screen.width, Screen.height * (1.09/6.3)),spos, Rect (0, 0, 420, 400));
        GUI.Box(Rect(.3,.01,Screen.width, Screen.height * (4.5/6.1)),
"	Your group owns a pet store. You have 24 feet of fencing and four corner posts to make a new pen in the stores backyard for the shipment of  rabbits you will be getting in next week." );

        GUI.ScrollTo(Rect (0,aa,100,20));
        bb=0;

        GUI.EndScrollView ();

        wnote();

        GUI.skin = uin;
        if(btn == 1)
        {
            aa=0      //box's y value 0  back to original position
            table = 1;

             abc=2;
        }

           }
           if(abc == 0)
            {
                wait();
                }

    }///// if table == 0

in wnote() function btn=1 is present , it will works after an animation gets over

function Update() { if(bb==0) { aa+=0.2; //scroll box vertically } }

declare another variable if(ee ==1){

scroll to }

once finished the background voice over ee =2;

while back button presses change ee value again to 1