asp.net problems with database connection strings in LINQ _ Practical Tips

Project I took a three-tier structure, I put the LINQ mapping file into the DAL layer, mapping file automatically generated by VS2008, the original machine has been normal, a little problem, when I moved the program to another machine above, the situation has changed, how are not connected to the database, This problem toss me for several days, changed the DAL under the app.config, also changed the web under the Web.config but no effect, a connection to the database on the error Timeout expired error, depressed for several days, Finally, the original database connection string was found in the LINQ mapping file as the setting.setting under the properties of the call, found the problem, modified the connection string, and immediately there was no problem.