Panel Tools Fails to start after 3.5 Upgrade

If you upgrade Panel Tools from 3.3-x to version 3.5 or later you may see the following error message when trying to run Panel Tool, and Panel Service will fail to start.

This may be caused by the following two scenarios:

• The server has .NET framework 4.5.2 and needs to be upgraded to 4.6.1 or newer
• The server has a custom schedule step dll which needs to be re-compiled against the current version of Panel Tools.

If the problem is a .NET version issue the error message will look like one of the following:

Application: PanelTool.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.MissingMethodException
Stack:
   at SoftwareIDM.PanelTool.Tool.Init()
   at SoftwareIDM.PanelTool.Tool.Run(System.String[])
   at SoftwareIDM.PanelTool.Program.Main(System.String[])


Service cannot be started. System.TypeInitializationException: The type initializer for 'SoftwareIDM.PanelClient.Helpers.Util' threw an exception. ---> System.TypeLoadException: Could not load type 'System.AppContext' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
   at SoftwareIDM.PanelModel.Helpers.Conf.get_Configuration()
   at SoftwareIDM.PanelClient.Helpers.Util.GetNow(Boolean local) in C:\SoftwareIDM\IdentityPanel\src\SoftwareIDM.PanelClient\Helpers\Util.cs:line 98
   at SoftwareIDM.PanelClient.Helpers.Util..cctor() in C:\SoftwareIDM\IdentityPanel\src\SoftwareIDM.PanelClient\Helpers\Util.cs:line 140
   --- End of inner exception stack trace ---
   at SoftwareIDM.PanelClient.Helpers.Util.RegisterKnownTypes() in C:\SoftwareIDM\IdentityPanel\src\SoftwareIDM.PanelClient\Helpers\Util.cs:line 31
   at SoftwareIDM.PanelService.Tool.Run() in C:\SoftwareIDM\IdentityPanel\src\SoftwareIDM.PanelService\Tool.cs:line 95
   at SoftwareIDM.PanelService.Service.OnStart(String[] args) in C:\S...