Request.QueryString producing corrupt value

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Data.OleDb;
using System.Web.Security;
using System.Configuration;
using User;
using Db;
 
namespace ChefMaha
{
	/// <summary>
	/// Summary description for fooditems.
	/// </summary>
	public class fooditems : System.Web.UI.Page
	{
		protected System.Data.OleDb.OleDbCommand FoodListOleDbCommand;
		protected System.Web.UI.WebControls.DataList FoodDataList;
		protected static System.Data.OleDb.OleDbConnection ChefMahaOleDbConn;
		protected static string ConnectionStr;
		protected static System.Data.OleDb.OleDbCommand FoodOleDbCommand;
		protected System.Web.UI.WebControls.DropDownList CategoryDropDownList;
		protected string ConnectionPhysicalPath;
		protected System.Data.OleDb.OleDbCommand CategoryOleDbCommand;
		protected static string SelectAllFromFood;
 
 
		private void Page_Load(object sender, System.EventArgs e)
		{
			
			if(!IsPostBack)
			{
				//set connection string
				ConnectionPhysicalPath = Server.MapPath("~/db/ChefMaha.mdb");
				ConnectionStr = ConfigurationSettings.AppSettings.Get("ConnectionString") + ConnectionPhysicalPath;
				SelectAllFromFood = FoodOleDbCommand.CommandText;
				
				ChefMahaOleDbConn = new OleDbConnection(ConnectionStr);
 
				LoadDropDownListWithData();
			}
 
			GetChosenCategory();
 
			LoadDataListWithData();
 
		}
 
		
		private void LoadDataListWithData()
		{
 
			if(ChefMahaOleDbConn.State.ToString() == "Closed")
			{
				ChefMahaOleDbConn.Open();
			}
							
			FoodOleDbCommand.Connection = ChefMahaOleDbConn;
 
			OleDbDataReader FoodDataReader = FoodOleDbCommand.ExecuteReader();
			FoodDataList.DataSource = (object) FoodDataReader;
			FoodDataList.DataBind();
				
			ChefMahaOleDbConn.Close();
		}
 
		/// <summary>
		/// gets the category chosen by the user
		/// </summary>
		private void GetChosenCategory()
		{
			string Category;
 
			try
			{
				Category = Request.QueryString["Category"].ToString();	
			}	
		
			catch(NullReferenceException)			
			{ 
				return;
			}
 
			ModifySelectedCategory(Category);
		}
 
 
		/// <summary>
		/// modifies the SQL statement of the menu grid according to the selected category
		/// </summary>
		/// <param name="SelectedCategory">the category selected by the user</param>
		private void ModifySelectedCategory(string SelectedCategory)
		{
			if(SelectedCategory == "All")
			{
				FoodOleDbCommand.CommandText = SelectAllFromFood;
			}
 
			else
 
			{
				string AppendedToSelectCmd = "WHERE FCtgEn = ";
 
				try
				{
					string NewValue = AppendedToSelectCmd + "'" + SelectedCategory + "'";
 
					FoodOleDbCommand.CommandText = SelectAllFromFood.Replace("ORDER BY FCtgEn", NewValue); 
				}
				catch(NullReferenceException)
				{
					foreach (Control c in Page.Controls)
					{
						c.Visible=false; 
					}
 
					Response.Write("An Error Occurred. Please refresh the Page.");
				}
			}
		
			LoadDataListWithData();
 
			if(CategoryDropDownList.SelectedValue != SelectedCategory)
			{
				try
				{
					CategoryDropDownList.SelectedValue = SelectedCategory;
				}
 
				catch(Exception ex)
				{
					for(int i=0; i<CategoryDropDownList.Items.Count; i++)
					{
						Response.Write(CategoryDropDownList.Items[i].Value);
					}
				}
			}
 
		} 
 
		
 
		/// <summary>
		/// loads the category drop down list with the categories from db
		/// </summary>
		private void LoadDropDownListWithData()
		{
 
				ChefMahaOleDbConn.Open();
			
 
			CategoryOleDbCommand.Connection = ChefMahaOleDbConn;
 
			OleDbDataReader CategoryDataReader = CategoryOleDbCommand.ExecuteReader();
		
			while(CategoryDataReader.Read())
			{
				string Category = CategoryDataReader.GetString(0);
				string CategoryEn = CategoryDataReader.GetString(1);
 
				ListItem CategoryListItem = new ListItem(Category, CategoryEn);
				CategoryDropDownList.Items.Add(CategoryListItem);
			}
 
			CategoryDataReader.Close();
 
			ChefMahaOleDbConn.Close();
		}
 
		private void CategoryDropDownList_SelectedIndexChanged(object sender, System.EventArgs e)
		{
 
			ChefMahaOleDbConn.Open();
		
			ModifySelectedCategory(CategoryDropDownList.SelectedValue);
 
			ChefMahaOleDbConn.Close();
		}
 
		#region Web Form Designer generated code
		override protected void OnInit(EventArgs e)
		{
			//
			// CODEGEN: This call is required by the ASP.NET Web Form Designer.
			//
			InitializeComponent();
			base.OnInit(e);
		}
		
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{    
			FoodOleDbCommand = new System.Data.OleDb.OleDbCommand();
			this.CategoryOleDbCommand = new System.Data.OleDb.OleDbCommand();
			this.CategoryDropDownList.SelectedIndexChanged += new System.EventHandler(this.CategoryDropDownList_SelectedIndexChanged);
			// 
			// FoodOleDbCommand
			// 
			FoodOleDbCommand.CommandText = "SELECT FCtg,  FCtgEn, FName, FUnit, FUnitPrice, FDescr, FPhoto FROM FOOD ORDER BY" +
				" FCtgEn";
			// 
			// CategoryOleDbCommand
			// 
			this.CategoryOleDbCommand.CommandText = "SELECT DISTINCT FCtg , FCtgEn FROM FOOD;";
			this.Load += new System.EventHandler(this.Page_Load);
 
		}
		#endregion
 
		
	}
}