Question

I have installed vs 2011 developer preview side by side with vs 2010. Now when i run my asp.net mvc 3 project in vs 2010 I am getting the following error in my project where i am using ModelClientValidationRule.

The type System.Web.Mvc.ModelClientValidationRule exists in both
c:\Program Files\Microsoft ASP.NET\ASP.NET MVC
3\Assemblies\System.Web.Mvc.dll and c:\Program Files\Microsoft
ASP.NET\ASP.NET Web Pages\v2.0\Assemblies\System.Web.WebPages.dll

Is this related to vs 2011 conlict with vs 2010 or something else

Answer 1

please see the below release notes :

http://www.asp.net/learn/whitepapers/mvc4-release-notes

Installing ASP.NET MVC 4 Developer Preview breaks ASP.NET MVC 3 RTM
applications.

ASP.NET MVC 3 applications that were created with the RTM release (not
with the ASP.NET MVC 3 Tools Update release) require the following
changes in order to work side-by-side with ASP.NET MVC 4 Developer
Preview. Building the project without making these updates results in
compilation errors.

http://www.asp.net/learn/whitepapers/mvc4-release-notes#_Toc303253815