Calling BRE policy in code from Orchestration

We are using the code below in an expression shape to call a BRE policy. We are not getting the expected results in the XML message. The policy works if we use the Call Rule shape.

Policy = new Microsoft.RuleEngine.Policy("CBSEAI_TE");

Policy.Execute(NotificationEvent);

Policy.Dispose();

 Any ideas

 Thanks in advance

Harold