having problem in running software on client side

See more:

.NET3.5

.NET

SQL-Server-2008

I have this connection string

connectionString = "Data Source=.;Integrated Security=SSPI;Initial Catalog=sms;Persist Security Info=False;Connect Timeout=60";

And, its running perfectly on my system.

But, when i run the software with this connection string on my client's system. I am getting an error as "A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)"

In my client's system sql server 2008 has an instance name "SQLEXPRESS" and changed the connection string to

connectionString = "Data Source=.\\SQLEXPRESS;Integrated Security=SSPI;Initial Catalog=sms;Persist Security Info=False;Connect Timeout=60";

but the result was the same error.

Please tell how can i resolve this problem.