I recently added log4net logging to this website. After configuring log4net and adding logging code the the web application, I immediately added a page to my administration site to display the log. Unfortunately, the initial code I wrote threw an exception because, not surprisingly, the log4net log file was locked.

The trick is to open the file in FileShare.ReadWrite mode:

...

protected string logFileText;

protected void Page_Load(object sender, EventArgs e)
{
    string path = Server.MapPath("~/logs/log.txt");

    using (FileStream fileStream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    using (StreamReader streamReader = new StreamReader(fileStream))
    {
        logFileText = streamReader.ReadToEnd();
    }
}

...