Not able to pass value in combo box allowing text value as well

[Aniket Bhoir]

My code is 

                driver.Manage().Timeouts().ImplicitWait = TimeSpan.FromSeconds(8000);

                IWebElement territory = driver.FindElement(By.XPath(".//*[@id='willis_willisterritoryid']/div[1]"));

               territory.Click();

                territory.Clear();

                driver.Manage().Timeouts().ImplicitWait = TimeSpan.FromSeconds(1000);

                territory.SendKeys("I");

            

I have a combo box which allows the user to input text from user and search the list of items from dropdown list. Currently i am able to select the field but not able to send keys.

Appreciate if any one could help me out.