Disable parallel build

Rx.NET/Source/build-new.ps1

@@ -52,7 +52,14 @@ msbuild "$scriptPath\System.Reactive.sln" /m /t:restore /p:Configuration=$config
 msbuild "$scriptPath\System.Reactive.sln" /m /t:restore /p:Configuration=$configuration
 
 Write-Host "Building $scriptPath\System.Reactive.sln" -Foreground Green
-msbuild "$scriptPath\System.Reactive.sln" /m /t:build /p:Configuration=$configuration 
+msbuild "$scriptPath\System.Reactive.sln" /t:build /p:Configuration=$configuration 
+if ($LastExitCode -ne 0) { 
+        Write-Host "Error with build" -Foreground Red
+        if($isAppVeyor) {
+          $host.SetShouldExit($LastExitCode)
+        }  
+}
+
 
 Write-Host "Building Packages" -Foreground Green
 msbuild "$scriptPath\src\System.Reactive\System.Reactive.csproj" /t:pack /p:Configuration=$configuration /p:PackageOutputPath=$artifacts /p:NoPackageAnalysis=true /p:NuGetBuildTasksPackTargets="workaround"
@@ -139,4 +146,4 @@ else
 {
   .\packages\ReportGenerator\tools\ReportGenerator.exe -reports:"$outputFile" -targetdir:"$outputPath"
   &"$outPutPath/index.htm"
-}
+}