Web Forms :: Not Executing And If (readingPos[k] == TextboxPos[k]) In This Line Giving Error Index Is Out Of Bond Array

This is my code for checking the spelling written in text box is correct or not.

But it is not working, it is not executing and if (readingPos[k] == TextboxPos[k]) in this line giving error index is out of bond array.

protected void Button2_Click(object sender, EventArgs e)
{
string j = TextBox1.Text;//TextBox1.Text =
_dictionary(j) ;
}
public string _dictionary(string word)
{
string[] wordArray = new string[125896];
string reading;
int nwords = 0;
FileStream fs = new FileStream(@"C:Documents and Settingsharsha.limayeDesktopspelling.txt", FileMode.Open, FileAccess.Read);
StreamReader s = new StreamReader(fs);
while((reading=s.ReadLine())!=null)
{
char[] TextboxPos=reading.ToLower().ToCharArray();
char[] readingPos = new char[20];
readingPos = TextBox1.Text.ToLower().ToCharArray();
if (TextboxPos[0] == readingPos[0])
{
//int[] save = new int[20];
int save = 0;
for (int k = 1; k < reading.Length; k++)
{
if (readingPos[k] == TextboxPos[k])
{ }
else
save += k;
}
if (save !=0 && save < 3)
{
TextBox1.Text = "Search for this" + reading;
break;
}
}
wordArray[nwords] = reading;
nwords++;
}