Error after move to Windows 2012 R2 server

Hi,

I have to identical websites with a custom made membership control based on the default ASP.NET membership components. I moved it to a new Windows 2012 R2 server. It is an exact copy of the old website which was on Windows 2008 R2.  Based on my investigation everything on IIS is configured identical on the new server. Everything on the website works perfectly, except on little thing. When the users try to activate their account this error is prompted on the new web server. The old server, with exact the same code works fine.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   MyServices.Membership.WXMembership.EncodePassword(String sPassword) +171
   MyServices.Membership.WXMembership.Activation(String sUsername, String sNewPassword, String sValidationCode) +918
   welcome.Validation() in C:\admin1\welcome.aspx.vb:64
   welcome.btnValidate_Click(Object sender, EventArgs e) in C:\admin1\welcome.aspx.vb:85
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +154
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3803

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34212 

It there something that can cause this from happing, What would be the most likely reason? Another function from the same assembly works fine. I compared the code letter per letter and it is exactly the same. Application pool and security is set correct.

The values String sUsername, String sNewPassword, String sValidationCode have a value when I do a response.write at the beginning of the function.

Thank you!