Earlier I posted about this problem I had with NHibernate, SQL CE 3.5.1.0 & ClickOnce. Well I found a workaround and it is very simple.

Instead of setting the "System.Data.SqlServerCe" reference property "Copy Local" to True,  when you are ready to deploy, set that reference property to false and on the ClickOnce Publish menu click on the "Application Files" button and change it from "Prerequisite (Auto)" to "Include".

You still have to set the "System.Data.SqlServerCe" reference property "Copy Local" to True while debugging your application locally for Nhibernate to work properly.

Remember to set it to false before publishing your application if not ClickOnce will remind you with the dreaded System.ArgumentException when launching the application.