I want to use multiple DSN connection string in my web.config file.
But its giving error as default driver not specified.
Any one please help me
That means that the connection string you are specifying is trying to connect to a database type and you have not added a reference to the drive to connect to that db type.
Tell us what DB you are trying to connect to and which code platform you are using at the very least to try and help you further.
A lot more info would help.