An exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll

There are some problems with your code. First I advise to use parametrized queries so you avoid SQL Injection attacks and also parameter types are discovered by framework:

var cmd = new SqlCommand("SELECT EmpName FROM Employee WHERE EmpID = @id", con);cmd.Parameters.AddWithValue("@id", id.Text);

Second, as you are interested only in one value getting returned from the query, it is better to use ExecuteScalar:

var name = cmd.ExecuteScalar();if (name != null){   position = name.ToString();   Response.Write("User Registration successful");}else{    Console.WriteLine("No Employee found.");}

The last thing is to wrap SqlConnection and SqlCommand into using so any resources used by those will be disposed of:

string position;using (SqlConnection con = new SqlConnection("server=free-pc\\FATMAH; Integrated Security=True; database=Workflow; ")){  con.Open();  using (var cmd = new SqlCommand("SELECT EmpName FROM Employee WHERE EmpID = @id", con))  {    cmd.Parameters.AddWithValue("@id", id.Text);      var name = cmd.ExecuteScalar();      if (name != null)    {       position = name.ToString();       Response.Write("User Registration successful");    }    else    {        Console.WriteLine("No Employee found.");    }  }}

I think your EmpID column is string and you forget to use ' ' in your value.

Because when you write EmpID=" + id.Text, your command looks like EmpID = 12345 instead of EmpID = '12345'

Change your SqlCommand to

SqlCommand cmd = new SqlCommand("SELECT EmpName FROM Employee WHERE EmpID='" + id.Text +"'", con);

Or as a better way you can (and should) always use parameterized queries. This kind of string concatenations are open for SQL Injection attacks.

SqlCommand cmd = new SqlCommand("SELECT EmpName FROM Employee WHERE EmpID = @id", con);cmd.Parameters.AddWithValue("@id", id.Text);

I think your EmpID column keeps your employee id's, so it's type should some numerical type instead of character.

Try this

SqlCommand cmd = new SqlCommand("SELECT EmpName FROM Employee WHERE EmpID=@id", con);cmd.Parameters.AddWithValue("id", id.Text);