EPiServer.Configuration.Settings.Instance - Application is initialized with settings for siteId="x", but current request maps to siteId="y"

We have a EPiServer 5.x enterprise project with several sites declared in EPiServer.config

These are set up as separate websites in IIS pointing at the same webroot matching the host entry for each IIS site to the siteHosts declared for each site in EPiServer.config

<site description="Site 1" siteId="SiteOne">
  <siteHosts>
    <add name="www.siteone.se" language="sv" />
    <add name="*"/>
  </siteHosts>
  <siteSettings .../>
</site>

<site description="Site 2" siteId="SiteTwo">
  <siteHosts>
    <add name="www.sitetwo.fi" language="fi" />
  </siteHosts>
  <siteSettings .../>
</site>

A problem we have been experiencing is that whenever we restart one or more of the sites in IIS and navigate to that site in a browser it (seemingly randomly) throws an error and logs:

Application is initialized with settings for siteId="SiteOne", but current request maps to siteId="SiteTwo"

if looking into the class "EPiServer.Configuration.Settings" below I can see that if the current request host does not match any of siteHost entry in EPiServer.config it will default to the siteHost site with the wildcard "*" instead.

At least one <site> section must omit the <siteHosts> section, or <add name=\"*\"> to the <siteHosts> section.

Question: Why would this happen? The sites in IIS are configured to listen to separate IP's and are bound to specific hosts.

Question: Since the EPiServer.Configuration.Settings.Instance has a public setter, would it be a good idea to be able to set this manually later? (via some .aspx or whatnot instead of restarting the application)

Of course it would be better to get a permanent fix to this instead of hacking together some half baked .aspx fix.

From the class "EPiServer.Configuration.Settings" :

public static Settings Instance
{
    get
    {
        if (HttpContext.Current == null)
        {
            if (_instance == null)
            {
                throw new ApplicationException("First time you call Settings.Instance you must have a valid HttpContext.");
            }
            return _instance;
        }
        Settings settings = MapUrlToSettings(HttpContext.Current.Request.Url);
        if (_instance == null)
        {
            _instance = settings;
        }
        else if (_instance != settings)
        {
            throw new ConfigurationErrorsException(string.Format("Application is initialized with settings for siteId=\"{0}\", but current request maps to siteId=\"{1}\"", _instance.Parent.SiteId, settings.Parent.SiteId));
        }
        return _instance;
    }
    set
    {
        _instance = value;
    }
}

public static Settings MapUrlToSettings(Uri url)
{
    Settings settings;
    if (url == null)
    {
        throw new ArgumentNullException("url", "An initialized Uri instance is required.");
    }
    if (!url.IsAbsoluteUri)
    {
        throw new ArgumentException("The Uri must be absolute to use for mapping.", "url");
    }
    if (!string.IsNullOrEmpty(url.DnsSafeHost))
    {
        settings = MapHostToSettings(url.DnsSafeHost, true);
    }
    else
    {
        settings = MapHostToSettings("*", true);
    }
    string absolutePath = url.AbsolutePath;
    string str2 = settings.SiteUrl.AbsolutePath;
    if (!absolutePath.StartsWith(str2, StringComparison.OrdinalIgnoreCase) && !string.Equals(absolutePath + "/", str2, StringComparison.OrdinalIgnoreCase))
    {
        throw new ConfigurationErrorsException(string.Format("The URL \"{0}\" maps to siteId=\"{1}\" but has a path that is outside the application root (application root is \"{2}\").", url.ToString(), settings.Parent.SiteId, settings.SiteUrl.AbsolutePath));
    }
    return settings;
}

public static Settings MapHostToSettings(string hostName, bool fallback)
{
    Settings settings;
    if (_hostToSettings == null)
    {
        InitializeAllSettings();
    }
    if (_hostToSettings.TryGetValue(hostName, out settings))
    {
        return settings;
    }
    if (!fallback)
    {
        return null;
    }
    return _hostToSettings["*"];
}

In EPiServer 6 and above, there is this irritating EPiServerFramework.config, which have a node called <automaticSiteMapping>. The first time you access a episerver site, it adds a key value that matches IIS site Id with the EPiServer site Id.

The most common cause for getting the "Application is initialized with settings for siteId..." error is that you for example have reinstalled your computer (or made a small change in the IIS...) and then setup your sites in a different order. For example site X has Id 1 the first time, but then gets Id 2. If you have site Y that used to have Id 2 and you have that mapped in your EPiServerFramework.config, then it will throw an exception.

The fastes way to get rid of this is

1. Find the IIS Id for the site you try to access
2. If you don't know your computer name, right click on 'Computer' and 'Properties' (and you will se Computer Name there)
3. Open EpiserverConfig and find the line with your computername and IIS Id, and you will notice that it is mapped to another site Id.
4. Remove that line.
5. Refresh the site.

I've encountered the same error before. I my case, we had multiple host headers configured for the sites in IIS, and one of these host headers was wrong according to the sitehosts definition in episerver.config.

If you use multiple host headers, double check them against the episerver.config files to assure they are configured on the same "sites"