Hi- I'm trying to use an external library DevExpress.XtraTreeList.v8.1.dll in my vsto office addin built using VS2010 beta 2. I am getting the following compile time error: DevExpress.Utils.AppareanceObject threw an exception -- System.NotSupportedException. The error message goes on to say that for compatibility reasons I can use the NetFx40_LegacySecurityPolicy switch. I've tried putting this config variable in all of the following locations: 1) my applications config file. 2) C:\Windows\Microsoft.NET\Framework\v4.0.21006\msbuild.exe.config 3) C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\dev.exe.config None of these have resolved the problem. Here were the references I've used. re-enable cas msdn.microsoft.com/en-us/library/ee191568(VS.100).aspx How do I get rid of this error so I can build the application in vs 2010?