I am consistently getting this error with VS 2013:
Could not copy \"C:\\pagefile.sys\" to \"bin\\roslyn\\pagefile.sys\". Exceeded retry count of 10.
As indicated in this answer from Pramod's comment the problem stems from the Microsoft.CodeDom.Providers.DotNetCompilerPlatform nuget package, specifically upgrading from version 1.0.0 to 1.0.1.
For me however, downgrading using Visual Studio caused further build errors. To solve the problem I had to manually edit my csproj and packages.config files, removing all references to Microsoft.Net.Compilers and Microsoft.CodeDom.Providers.DotNetCompilerPlatform.
Specifically, this meant:
sections for both versions of both libraries