The specified request cannot be executed from current Application Pool (403.18)

So you've split your apps into seperate app pools in IIS, which works well for app isolation on your web server and all is well until you start getting 403 HTTP status responses (with a substatus in the IIS logs of 18). This error is a result of your application running your application and the custom error page you've configured within different app pools.

The solution?

I'm afraid you're going to have to edit the registry!!! So back it up first then create a registry key with the name IgnoreAppPoolForCustomErrors, of type DWORD and value 1 under the HKLM\SYSTEM\CurrentControlSet\Services\W3SVC\Parameters\ folder.

A potentially dangerous Request.Form value was detected from the client

You'll get this error from the .Net framework when it detects potentially harmful content in a web request submission. Want to disable this validation? Read on...

For normal ASP.Net Web forms apps you can disable request validation by setting validateRequest=false in the page directive (top of your aspx page) or in the configuration section.

For ASP.Net MVC apps add the [ValidateInput(false)] attribute to the appropriate controller action.

Be careful when turning off this value as you are making your site vulnerable by accepting potentially harmful input. You should explicitly validate your input in your code if you disable the built in .Net request validation.

Read an Embedded Resource Text File in C#

Here's a little snippet I use quite a lot in my test projects to read out an embedded resource text file as a string. The resourceName parameter is the full namespace of the resource, e.g. myproject.files.MyEmbeddedTextFile.txt

internal string GetFromResources(string resourceName)
{
    Assembly assem = this.GetType().Assembly;
    using (Stream stream = assem.GetManifestResourceStream(resourceName))
    {
        using (var reader = new StreamReader(stream))
        {
            return reader.ReadToEnd();
        }
    }
}

P.S. You may want to add some error handling to the above ;)