Question

I developed a winforms app locally on my machine. It reads data from a csv file and looks up related information from a database (by executing a stored proc).

I moved that to the development server and tried running it, but I get an error when at the line that gets SQL connection string from app.config file. The error is: System.NullReferenceException: Object reference not set to an instance of an object.. Of course the app runs fine on my machine.

I commented out all lines following this code, and the error message is displayed. I am guessing it has to do with the conn.ConnectionString line.

The SQL database is pointing to the correct db server & UID & pwd are correct. What would be causing the error?

    try
    {
        using (SqlConnection conn = new SqlConnection())
        {
            conn.ConnectionString = ConfigurationManager.ConnectionStrings["SilverTicker"].ConnectionString;

Answer 1

One of the objects in your code sample is returning “null”. I’m guessing that it’s

ConfigurationManager.ConnectionStrings["SilverTicker"].ConnectionString

Put a breakpoint on that line and check the contents of the .ConnectionStrings collection to be sure that it contains “SilverTicker”.

I’m guessing that ConfigurationManager.ConnectionStrings["SilverTicket"] is undefined (probably because of an inconsistency between app.config in the two environments), so accessing it’s .ConnectionString property is throwing an exception.