I used git to download the latest version of APM. When I try to build it, I get warnings on trying to open the MainV2.cs, but I still went ahead and tried to build, there are build errors.

I have a feeling that I am missing something very basic here. I still can build older versions of APM, so I am wondering if I am missing out on something basic out here. Any suggestions invited.

The first three are warnings from trying to open MainV2.cs. The rest are build errors.

Warning    1    Could not find type 'ArdupilotMega.Controls.ToolStripConnectionControl'.  Please make sure that the assembly that contains this type is referenced.  If this type is a part of your development project, make sure that the project has been successfully built using settings for your current platform or Any CPU.        0    0    
Warning    2    The variable 'toolStripConnectionControl' is either undeclared or was never assigned.    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\MainV2.Designer.cs    64    0    
Warning    3    The predefined type 'System.Runtime.CompilerServices.ExtensionAttribute' is defined in multiple assemblies in the global alias; using definition from 'c:\apmsrc\may28\Tools\ArdupilotMegaPlanner\bin\Release\Microsoft.Scripting.ExtensionAttribute.dll'    ArdupilotMega
Error    4    The type or namespace name 'Reactive' does not exist in the namespace 'System' (are you missing an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\IMAVLink.cs    3    14    ArdupilotMega
Error    5    The type or namespace name 'Reactive' does not exist in the namespace 'System' (are you missing an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\MAVLink.cs    3    14    ArdupilotMega
Error    6    The type or namespace name 'Reactive' does not exist in the namespace 'System' (are you missing an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    4    14    ArdupilotMega
Error    7    The type or namespace name 'Reactive' does not exist in the namespace 'System' (are you missing an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    5    14    ArdupilotMega
Error    8    The type or namespace name 'Reactive' does not exist in the namespace 'System' (are you missing an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    6    14    ArdupilotMega
Error    9    The type or namespace name 'CompositeDisposable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    15    17    ArdupilotMega
Error    10    The type or namespace name 'Subject' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\IMAVLink.cs    40    9    ArdupilotMega
Error    11    The type or namespace name 'Subject' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\IMAVLink.cs    41    9    ArdupilotMega
Error    12    The type or namespace name 'Subject' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\MAVLink.cs    65    26    ArdupilotMega
Error    13    The type or namespace name 'Subject' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\MAVLink.cs    66    26    ArdupilotMega
Error    14    The type or namespace name 'IObservable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\MAVLink.cs    71    16    ArdupilotMega
Error    15    The type or namespace name 'IObservable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\MAVLink.cs    76    16    ArdupilotMega
Error    16    The type or namespace name 'Subject' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\MAVLink.cs    83    16    ArdupilotMega
Error    17    The type or namespace name 'Subject' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\MAVLink.cs    85    16    ArdupilotMega
Error    18    The type or namespace name 'IObservable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\IMAVLink.cs    115    9    ArdupilotMega
Error    19    The type or namespace name 'IObservable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Mavlink\IMAVLink.cs    116    9    ArdupilotMega
Error    20    The type or namespace name 'IObservable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    129    24    ArdupilotMega
Error    21    The type or namespace name 'IObservable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    129    82    ArdupilotMega
Error    22    The type or namespace name 'Subject' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    129    110    ArdupilotMega
Error    23    The type or namespace name 'IObservable' could not be found (are you missing a using directive or an assembly reference?)    C:\apmsrc\may28\Tools\ArdupilotMegaPlanner\Controls\ConnectionStats.cs    165    67    ArdupilotMega
Warning    24    Could not resolve this reference. Could not locate the assembly "System.Reactive". Check to make sure the assembly exists on disk. If this reference is required by your code, you may get compilation errors.    ArdupilotMega
Warning    25    The referenced component 'System.Reactive' could not be found.