Mono Folder was not found

Thanks for the help.
Tried the setting with a bunch of different paths, now every time it says
“E: No access to the given key”
Would the target framework in the project be relevant here? Tried changing it to 4.5 but no diff.
Based on the error I tried running sudo ebuild ... , the errors changed to

E: Reference 'mscorlib' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'System' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'System.Data' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'System.Xml' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'System.Core' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'System.Xml.Linq' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'System.Data.DataSetExtensions' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'Swift' could not be resolved for target 'Echoes' (Echoes .NET anycpu).
E: Reference 'Echoes' could not be resolved for target 'Echoes' (Echoes .NET anycpu).

For any path I tried.
Maybe my mono install is borked? Or not whats expected, anyway. I did try an apt-get install again.

Under /usr/lib/mono is

2.0-api  3.5-api  4.0  4.0-api  4.5  4.5-api  aot-cache  gac  mono-configuration-crypto  monodoc  xbuild  xbuild-frameworks

under /usr/lib/mono/4.5 is:

Accessibility.dll                       Mono.Debugger.Soft.dll                       System.IO.Compression.FileSystem.dll
al.exe                                  Mono.Http.dll                                System.Json.dll
browsercaps-updater.exe                 monolinker.exe                               System.Json.Microsoft.dll
caspol.exe                              Mono.Management.dll                          System.Management.dll
etc etc

under 4.5-api is:

Accessibility.dll                       mscorlib.dll                               System.Reactive.Providers.dll
Commons.Xml.Relaxng.dll                 Novell.Directory.Ldap.dll                  System.Reactive.Runtime.Remoting.dll
cscompmgd.dll                           PEAPI.dll                                  System.Reactive.Windows.Forms.dll
CustomMarshalers.dll                    RabbitMQ.Client.dll                        System.Reactive.Windows.Threading.dll
etc etc