Can anyone help me?

I had a simple code:

```
private void ObterRelatorios(string id) { 
    var relatorios = new Dictionary<string, string>();

    var xml = new XmlDocument();

    xml.Load("my_path");

    foreach (XmlNode node in relatoriosStaticos.DocumentElement.ChildNodes)
        relatorios.Add(node.Attributes["Titulo"].InnerText, string.Concat(node.Attributes["Url"].InnerText, id));
}

```

My xml is quite simple with 5 nodes and always is the same.

This is wierd because sometimes works, sometimes not.

This is what I get when throw an exception

**Error Details:** 

```
Exception of type 'System.Web.HttpUnhandledException' was thrown.

```

**Full Stack:** 

```
[ArgumentNullException: Value cannot be null.
Parameter name: key]
at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
at System.Collections.Generic.Dictionary.Insert(TKey key, TValue value, Boolean add)
at System.Collections.Generic.Dictionary.Add(TKey key, TValue value)

```