Read A Specific Attribute From A Xml Website?

I'm tryign to read a specific attribute from a xml website using this code:

'this is the url im trying to read, tmpIn is a string that complete the url:
Dim url As String = "http://maps.google.com/maps/geo?q=" & tmpIn & "&output=xml"
Dim reader As New XmlTextReader(url)

[Code]....

The problem is tmpIn takes diferents values (string) when the function is used and sometimes this works, and othertimes it gives an error (Invalid character in the given encoding. Line 9, position 15.), but is not because of the url, is when it tries to read the coordinates...