After Upgrading DNN 7 and browsing to the ADMIN>Site Settings you find an error: A critical error has occurred. Object reference not set to an instance of an object.
FileHelpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=3e0c08d59cc3d657′
Error: File Management is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: (0): error CS1705: Assembly ‘DotNetNuke.Modules.DigitalAssets, Version=7.1.1.385, Culture=neutral, PublicKeyToken=null’ uses ‘Telerik.Web.UI, Version=2013.2.611.40, Culture=neutral, PublicKeyToken=121fae78165ba3d4′ which has a higher version than referenced assembly ‘Telerik.Web.UI, Version=2013.1.403.40, Culture=neutral, PublicKeyToken=121fae78165ba3d4′ —> System.Web.HttpCompileException: (0): error CS1705: Assembly ‘DotNetNuke.Modules.DigitalAssets, Version=7.1.1.385, Culture=neutral, PublicKeyToken=null’ uses ‘Telerik.Web.UI, Version=2013.2.611.40, Culture=neutral, PublicKeyToken=121fae78165ba3d4′ which has a higher version than referenced assembly ‘Telerik.Web.UI, Version=2013.1.403.40, Culture=neutral, PublicKeyToken=121fae78165ba3d4′ at System.Web.Compilation.AssemblyBuilder.Compile() at System.Web.Compilation.BuildProvidersCompiler.PerformBuild() at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath) at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) at System.Web.Compilation.BuildManager.GetVPathBuildResult(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean ensureIsUpToDate) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at DotNetNuke.UI.Modules.WebFormsModuleControlFactory.CreateModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleControlFactory.LoadModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl() — End of inner exception stack trace —
The problem
The problem relates to a missing file that can be updated to the website /bin folder. The file is part of a free library that can be found here: http://sourceforge.net/projects/filehelpers/files/File%20Helpers%20Downloads/Version%202.0.0/
The file you need is: FileHelpers.dll front he 2.0 release from way back in 2010.
The Fix
Download the file directly here: https://dl.dropboxusercontent.com/u/6726341/FileHelpers.dll
And save that to the /BIN folder in your DNN website, this will fix the issue and leave any third party modules that reference it working. 
