Please help!

so, I got a error, a compilation error. on unity 4.6.6

Could not start compilationApplicationException: Unable to find csharp compiler in C:/Users/levi/Desktop/Unity/Data/Mono\lib/mono/unity_web
UnityEditor.Scripting.Compilers.MonoCSharpCompiler.GetCompilerPath (System.Collections.Generic.List`1 arguments) (at C:/buildslave/unity/build/Editor/Mono/Scripting/Compilers/MonoCSharpCompiler.cs:73)
UnityEditor.Scripting.Compilers.MonoCSharpCompiler.StartCompiler () (at C:/buildslave/unity/build/Editor/Mono/Scripting/Compilers/MonoCSharpCompiler.cs:44)
UnityEditor.Scripting.Compilers.ScriptCompilerBase.BeginCompiling () (at C:/buildslave/unity/build/Editor/Mono/Scripting/Compilers/ScriptCompilerBase.cs:47)

windows 8 directX 11
snapshot:

When exactly did these errors appear? As in, what were you doing immediately before you got these errors?