In our ASP.NET MVC application, we\'ve noticed that we cannot have The Forbidden DOS File Names—COM1 through COM9, LPT1 through
COM1
COM9
LPT1
This has been addressed in ASP.NET 4. http://haacked.com/archive/2010/04/29/allowing-reserved-filenames-in-URLs.aspx
You can apply a setting in web.config that relaxes this restriction.
Hope that helps.