Unity4.6 to Unity5 Problems - System.TypeLoadException

Hello. I have a project that is underway for the last 3 years, I have been using unity without any problems. Recently, unity5 was released and I want to start using it with my project (hopefully it will also fix numerous unity crashes, since my project is very big and i believe its crashing the editor all the time because it runs out of memory, changing to 64bit editor might solve that). When I open my project in unity5, I get the following errors : --- > Unhandled Exception: System.TypeLoadException: A type load exception has occurred.> at Mono.CSharp.Driver.ParseArguments (System.String[] args, Boolean require_files) [0x00000] in :0 > at Mono.CSharp.Driver.Create (System.String[] args, Boolean require_files, Mono.CSharp.ReportPrinter printer) [0x00000] in > :0 at Mono.CSharp.Driver.Main (System.String[] args) [0x00000] in :0 -- > Failed to load package manager> UnityEditor.Modules.ModuleUtils:GetAdditionalReferencesForUserScripts() -- And I am clueless about how to resolve it. I have searched online but I havent found anything pointing towards a solution. Hopefully, someone knows how to resolve this.