Visual C# and SQL Server Express

I wrote an application on my home machine using Visual Studio and SQL Server. The application runs fine. This application needed to be installed on a server for a company.I copied the executable and the library files to the company server. The Machine is a Windows 2003 Small Business Server with SQL Server engine installed already. So I installed SQL Server Express to be able to use the Engine and build my database on the server.When I ran the executable it would not connect to the server even though I changed the settings in the connection string to the sql server on the SBS Server.I installed Visual C# Express on the machine to debug the application and I can not get the data source to connect to the SQL Server.I get the following error SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specifiedany help will be extremely appreciated. thank you