I think the issue was by ths following , Yes, of course, if both programs run on the same computer and the database file resides on a local drive. SQL Server Compact supports up to 256 connections. Make sure to use the exact same connection string from both processes.
Can't add SQL Compact Edition to my VB.net Application
may help you . Yes, you can include it as an embedded resource, but you must write it to disk before you can use it from your app. You can backup by stopping all threads using the database and performing a file copy.
Issue connecting to SQL Compact Edition on Windows Mobile 6 Emulator