Problems with database connection strings in asp.net LINQ

Project I used three layer structure, I put LINQ mapping file DAL this layer, the mapping file generated by VS2008 automatically, in the original machine 1 straight normal, 1 point problem all have no, when I moved to another 1 computer the program above, the situation is changed, how can't connect database, the problem with me for several days, changed under DAL app. config, also changed under Web web. config but have no effect, 1 connection to the database reported this error Timeout expired error, depressed for several days, finally from the LINQ mapping file found that the original database connection string 1 is directly called Properties Setting.Setting, find the problem, modify the connection string, immediately there is no problem.