There is no argument given that corresponds to the required formal parameter - .NET Error

Solution 1:

In the constructor of

public class ErrorEventArg : EventArgs

you have to add "base" as follows:

public ErrorEventArg(string errorMsg, string lastQuery) : base (string errorMsg, string lastQuery)
{
    ErrorMsg = errorMsg;
    LastQuery = lastQuery;
}

Solution 2:

You have a constructor which takes 2 parameters. You should write something like:

new ErrorEventArg(errorMsv, lastQuery)

It's less code and easier to read.

EDIT

Or, in order for your way to work, you can try writing a default constructor for ErrorEventArg which would have no parameters, like this:

public ErrorEventArg() {}

Solution 3:

I got the same error but it was due to me not creating a default constructor. If you haven't already tried that, create the default constructor like this:

public TestClass()
{
}