I don't understand why this is happening...Please help

Question

I am having a problems on one of my C# forms but can't figure out why. This characteristic only occurs on one form in my project. The others forms do not have this symptom. When I change the DropDownStyle property to "DropDownList" from "DropDown". I get the following error when I attempt to run the program. C:\TracerApplications\MTOSuite\MTO.cs(1063): 'System.Windows.Forms.TextBox' does not contain a definition for 'Windows' line 1063 is: this.JacketMaterial.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList; If I manually remove the "System.Windows.Forms" and leave it as: this.JacketMaterial.DropDownStyle = ComboBoxStyle.DropDownList; It will run fine until I change another property on the form and rebuild my app. This happens on every item I have set to DropDownList. This is only happening on one form. My other forms build fine with Dropdownlsit selected and I cannot determine why. My using statements include: using System; using System.Drawing; using System.Collections; using System.ComponentModel; using System.Windows.Forms; using System.Data; using ProjectClass; using System.Reflection; Is there way way that I can prevent rebuilding the code, for each control, everytime I rebuild? Does anyone have any ideas? Thanks in advance for your help.