How to fix them
Usage of "var" allows for cleaner code, but it also makes it easier to write code that is harder to maintain.
Visual Studio RegEx
The Visual Studio RegExp syntax is not entirely standard. These are the most basic differences.
ASP.NET Url Rewriting and Postbacks
When using url rewriting in combination with asp.net, postbacks tend not to go to the rewritten url but to the underlying real url. Since .NET 3.5 SP1 this is easily fixed.