Suggest do this in your code-behind before sending down to SQL Server.
int userVal = int.Parse(txtboxname.Text);
Perhaps try to parse and optionally let the user know.
int? userVal;
if (int.TryParse(txtboxname.Text, out userVal)
{
DoSomething(userVal.Value);
}
else
{ MessageBox.Show("Hey, we need an int over here."); }
The exception you note means that you're not including the value in the call to the stored proc. Try setting a debugger breakpoint in your code at the time you call down into the code that builds the call to SQL Server.
Ensure you're actually attaching the parameter to the SqlCommand.
using (SqlConnection conn = new SqlConnection(connString))
{
SqlCommand cmd = new SqlCommand(sql, conn);
cmd.Parameters.Add("@ParamName", SqlDbType.Int);
cmd.Parameters["@ParamName"].Value = newName;
conn.Open();
string someReturn = (string)cmd.ExecuteScalar();
}
Perhaps fire up SQL Profiler on your database to inspect the SQL statement being sent/executed.