html textbox editor is disabled on postback??

Your code looks all fine. i could not run your code due to missing plugins for tinyMCE, but I ran a sample page with a ddl having AutoPostback=True. see this example:

-----------------------------------------------------------------------

style="margin-top:5px;" TextMode="MultiLine"
Width="400px">
onselectedindexchanged="ddl1_SelectedIndexChanged" AutoPostBack="true">

---------------------------------

Code Behind:
--------------------------------
protected void Page_Load(object sender, EventArgs e)
{

}

protected void ddl1_SelectedIndexChanged(object sender, EventArgs e)
{
   Response.Write("");
}
----------------------------------------

It works like a charm, no issues. I suggest you to check if your plugins are getting loaded properly. use developer tools in chrome or IE whatever you prefer and diagnose the problem.

Hope it helps :)

  DataAccess.DAL objdal = new DataAccess.DAL();
    Hashtable hsinput = new Hashtable();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            bindstate();
            Bindddlcmpny();
        }

        txtjobpost.Attributes.Add("readonly", "readonly");


    }
    public void bindstate()
    {
        DataSet ds = new DataSet();
        ds = objdal.FillDataSet(CommandType.Text, "select * from state where active=1");
        //ddlstate.Items.Clear();
        //ddlstate.Items.Add("Select State");
        ddlstate.DataTextField = "statename";
        ddlstate.DataValueField = "StateId";
        ddlstate.DataSource = ds.Tables[0];
        ddlstate.DataBind();
        ddlstate.Items.Insert(0, new ListItem("-- Select State --", "0"));

    }
    public void Bindddlcmpny()
    {

        DataSet ds = new DataSet();
        ds = objdal.FillDataSet(CommandType.Text, "select ID,companyName from employerRegistration");
        ddlcmpny.DataTextField = "CompanyName";
        ddlcmpny.DataValueField = "ID";
        ddlcmpny.DataSource = ds.Tables[0];
        ddlcmpny.DataBind();
        ddlcmpny.Items.Insert(0, new ListItem("-- Select company --", "0"));
    }
 


i have bind the  dropdownlists on pageload  and on postback the html editor is not working.

and i am using for textbox


                   style="margin-top:5px;" TextMode="MultiLine"
                   Width="400px">

this code is working in another page but there is no any control like dropdown for postback