Security.Cryptography.Xml in Mobile Applications?

Hi,

I'm very basically tryint to encrypt an xml file stored locally on a pocketPC, using a example given on the msdn site.

using System.Security.Cryptography.Xml;

wont be recognised by my app, is this cos its a mobile app, or am i doing something completely wrong....

http://msdn2.microsoft.com/en-us/library/ms229746(VS.80).aspx being the tutorial...

anyone know a way of resolving this? or is there a better/easier method to achieve the encryption of a item in the xml at least, i.e a Password stored locally.