Can't connect to MsBuild project model process in 600000 ms

I submitted a bug report for this same issue. Rider EAP doesn't make it clear that Mono 4.6 is required.

$ /Applications/Rider\ EAP.app/Contents/lib/ReSharperHost/macos-x64/mono/bin/mono-sgen --version
Mono JIT compiler version 4.6.0 (mono-4.6.0.245/746756c Thu Sep 15 12:25:06 MSK 2016)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
 TLS: normal
 SIGSEGV: altstack
 Notification: kqueue
 Architecture: amd64
 Disabled: none
 Misc: softdebug
 LLVM: supported, not enabled.
 GC: sgen

This version conflicts with the installed version of mono:

$ mono --version
Mono JIT compiler version 4.2.3 (Stable 4.2.3.4/832de4b Wed Mar 30 13:57:48 PDT 2016)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
 TLS: normal
 SIGSEGV: altstack
 Notification: kqueue
 Architecture: amd64
 Disabled: none
 Misc: softdebug
 LLVM: supported, not enabled.
 GC: sgen

After updating mono to 4.6, I no longer received the error.

On Mac, installing via Mono's downloaded .pkg doesn't overwrite the brew version. If you've installed mono through brew, getting updated to 4.6 is pretty easy:

$ brew unlink mono

$ brew install mono

Doesn't work for me:

Exception from inside Rider:

Can't connect to MsBuild project model process in 600000 ms
 --- EXCEPTION #1/2 [InvalidOperationException]
 Message = “Can't connect to MsBuild project model process in 600000 ms”
 ExceptionPath = Root.InnerException
 ClassName = System.InvalidOperationException
 HResult = COR_E_INVALIDOPERATION=80131509
 Source = JetBrains.Platform.RdFramework
 StackTraceString = “
 at JetBrains.Platform.RdFramework.ExternalProcessModel.ProtocolModelExternalProcess`1[TModel].Run () [0x0023d] in <a9cb5d0db8d342f99a0d40f748ec1273>:0 
 at JetBrains.Platform.MsBuildHost.Impl.MsBuildExecutorFactory.Create (JetBrains.DataFlow.Lifetime lifetime, JetBrains.Platform.MsBuildHost.MsBuildExecutorContext context) [0x0003f] in <cc68c7333bd2464bac2891cf77e06a5f>:0 
 at JetBrains.ProjectModel.ProjectsHost.MsBuild.MsBuildSessionHolder.CreateSession () [0x000bd] in <ee075599af1b4bfb9a500ae496258efd>:0 
 at JetBrains.ProjectModel.ProjectsHost.MsBuild.MsBuildSessionHolder.Execute[T] (System.Func`2[T,TResult] executor) [0x0001b] in <ee075599af1b4bfb9a500ae496258efd>:0 
 at ... (show balloon)

$ /Applications/Rider\ EAP.app/Contents/lib/ReSharperHost/macos-x64/mono/bin/mono-sgen --version
Mono JIT compiler version 4.9.0 ((HEAD/57d1115 Thu Oct 20 18:16:53 MSK 2016)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
 TLS: normal
 SIGSEGV: altstack
 Notification: kqueue
 Architecture: amd64
 Disabled: none
 Misc: softdebug
 LLVM: supported, not enabled.
 GC: sgen (concurrent by default)

$ mono --version
Mono JIT compiler version 4.6.1 (Stable 4.6.1.5/ef43c15 Tue Oct 18 11:06:44 BST 2016)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
 TLS: normal
 SIGSEGV: altstack
 Notification: kqueue
 Architecture: amd64
 Disabled: none
 Misc: softdebug
 LLVM: supported, not enabled.
 GC: sgen

To be sure I (redundant) uninstalled and reinstalled mono with brew.

What part am I missing....

Rider may have detected and used non-brew mono, so it may be the key problem.

Please try to follow this link https://rider-support.jetbrains.com/hc/en-us/articles/207329790