One Package Two Configurations; App.LoadFromSqlServer(); Package.ImportConfigurationFile(Dev/Prod.dtsconfig);

Hi all,
I need one more help!
we can select the dtsconfig file with the Environment variable(indirect configuration);
but i need to select the configuration file at runtime; i've to load the package from the server and apply local configuration file to the package and run in a web server;

Requirements;
1. i have packages with its xml configurations for connection strings alone!
2. i deployed it on the server
3. Trying to execute the packages in a web page onclick event;

We have ASP.net WebPage; in On_Click Event, i have this code;

Application ap = new Application();
Package pk = ap.LoadFromSqlServer("\PROJECT", "itsssqldb", "pmo_package_user", "password", null);
pk.ImportConfigurationFile(@"Packagesdev_staging.dtsConfig");
pk.Execute();
here PROJECT is the Package name; i'm loading the package from the Common Sequel Server 2005; and applying the configuration file to that package and trying to execute this;
but its not using the config file what i mentioned; its returning failure!!

Can you please help me to resolve this issue!,

(The intention of doing this job is to select the configuration file( prod, dev) at runtime)