Upgrade to ASP.NET 4.0 for existing forum owners

If you have an existing forum running on ASP.NET 3.5 and wish to use the new ASP.NET 4.0 framework, you can perform an upgrade for the web.config file by opening the software with Visual Studio 2010 as a web site. The software will run fine under the 4.0 framework after the web.config file is free of any ASP.NET 3.5 specifics.
 
Once the software is loaded in VS 2010, on the Solution Explorer pane, right click on website -> Property Pages -> Build -> Target Framework and set the dropdown value to .NET Framework 4, and Visual Studio will help you upgrade the web.config file on your dev machine to ASP.NET 4.0. You can then upload this newly edited web.config from the dev machine to your site. Make sure the connectionString as well as the machineKey are set correctly before uploading.
 
There are a few things you need to be aware of when upgrading to ASP.NET 4.0 this way:

1. CDN for Telerik controls is not available (in the appSettings keys regarding CDN, you need to set the values to Disabled): This is a small issue bandwidth wise as the files are cached in browser;
2. Automatic or Manual recycling AppDomain through the software (appSettings keys or Admin CP) does not work due to the changes in the .NET framework. You can achieve the same effect by setting AppPool recycling via IIS, or use the touch trick (adding a space to web.config) to recycle the AppDomain if required.
3. under system.web -> httpRuntime, you need to make sure the requestValidationMode attribute is added and its value to 2.0, like the following:
   <httpRuntime maxRequestLength="19999" requestValidationMode="2.0" />