Reset password on Windows Server 2008 R2

Hi All,

We have an Employee Self Service application running on standalone server.
One of the feature of the application is "forgotten password", so employees can reset their own passwords.
It works fine an all servers, but not on Windows Server 2008 R2. Below is a fragment of code we use:

User.Invoke("SetPassword", new object[] {"#12345Abc"});
User.CommitChanges();

It looks like it is not possible to make it work in Windows Server 2008 R2 at all.
If someone has it works, please help.

Thanks