I added below settings in .sln.DotSettings
<s:String x:Key="/Default/CodeInspection/CSharpLanguageProject/LanguageLevel/@EntryValue">CSharp50</s:String>
This line was added to .csproj.DotSettings when I tried to disable c#6 for a particular project. After adding this line in .sln.DotSettings resharper is reporting an error whenever I am trying to use c# 6.0 feature.