When I was using ASP.NET with SQL Server CE I was getting following error.Unable to load the native components of SQL Server Compact corresponding to the ADO.NET provider of version 8080. Install the correct version of SQL Server Compact. Refer to KB article 974247 for more details.
In order to solve this error, I referenced the System.Data.SqlServerCe.dll from my Sql Server CE installation folder "F:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Desktop" and it worked for me. I have given this solution here as I found that on social msdn (http://social.msdn.microsoft.com/Forums/en/sqlce/thread/3988985f-5395-488e-af14-d44d2931fdfb) there is other solution provided but that doesn't work for me.
Hope this will help someone.