How do I get the linenumber from stacktrace in debug/release mode?

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C#

.NET

error-handling

Hello all,

My problem is that I cant get the linenumber of the frames in a stacktrace class from my website and log them to DB in my Global.asax file. The variable LineNumber is always zero (0).
I have checked that I have a PDB available in the applications bin folder.
So what do I have to do for getting the linenumbers? Is there something I need to write into my web.config - or to mention in project options or...?

Thanks in advance.
Michael

What I have tried:

protected void Application_Error(object sender, EventArgs e)
{
    Exception exc = Server.GetLastError();
    StackTrace st = new StackTrace(exc, true);
    foreach (StackFrame frame in st.GetFrames())
    {
        int LineNumber = frame.GetFileLineNumber();
    }
    Server.ClearError();
}