Service cannot be started. System.TypeLoadException: Could not load type Unify.Product.EventBroker.MIMReferenceRepository

The UNIYFNow service had failed to completely uninstall some months ago in a DEV environment.  On rebooting the service uninstall seems to have finally completed, leaving only the extensibility files in place and a few config files.  What I hadn't noticed was the presence of some old patches.  On removing these the service was finally able to restart - I recognised these files only by file date.

I am raising this purely for future reference for anyone else spinning their wheels on this sort of thing - and in the hope that there might be a KB article created to help out when this sort of thing happens and they don't have the necessary familiarity to work it out for themselves.

Log Name:      Application
Source:        UNIFYNow
Date:          22/08/2019 3:45:13 PM
Event ID:      0
Task Category: None
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      D-OCCCP-IM303.dbb.local
Description:
Service cannot be started. System.TypeLoadException: Could not load type 'Unify.Product.EventBroker.MIMReferenceRepository' from assembly 'Unify.EventBroker.Agents, Version=4.0.0.0, Culture=neutral, PublicKeyToken=84b9288cb2633de4'.
   at Unify.Product.EventBroker.AgentEngine..ctor(IConfigurationEngine configurationEngine, ILicensingEngine licensingEngine, INotificationMessageService messageService, IIsolatedStoredValuesEngine storedValuesEngine, IScheduleComposite scheduler, IEventBrokerBranding branding, IUnifyEnginePlugInKey plugInKey)
   at Unify.Product.EventBroker.AgentEnginePlugInFactory.CreateComponent(IUnifyEnginePlugInFactoryInformation`1 factoryInformation)
   at Unify.Framework.DependencyPlugInGenerator`4..ctor(ICollection`1 plugInGenerator, IPlugInFactory`2 factoryInformationFactory)
   at Unify.Framework.UnifyEngine`1..ctor(TBranding branding, IEnumerable`1 additionalPlugInFactories, DirectoryInfo executingAssemblyLocation, IsolatedStorageFile isolatedStorageLocation)
   at Unify.Product.EventBroker.EventBrokerSer...
Event Xml:
<event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <system>
    <provider name="UNIFYNow">
    <eventid qualifiers="0">0</eventid>
    <level>2</level>
    <task>0</task>
    <keywords>0x80000000000000</keywords>
    <timecreated systemtime="2019-08-22T05:45:13.639360700Z">
    <eventrecordid>535918</eventrecordid>
    <channel>Application</channel>
    <computer>D-OCCCP-IM303.dbb.local</computer>
    <security>
  </security></timecreated></provider></system>
  <eventdata>
    <data>Service cannot be started. System.TypeLoadException: Could not load type 'Unify.Product.EventBroker.MIMReferenceRepository' from assembly 'Unify.EventBroker.Agents, Version=4.0.0.0, Culture=neutral, PublicKeyToken=84b9288cb2633de4'.
   at Unify.Product.EventBroker.AgentEngine..ctor(IConfigurationEngine configurationEngine, ILicensingEngine licensingEngine, INotificationMessageService messageService, IIsolatedStoredValuesEngine storedValuesEngine, IScheduleComposite scheduler, IEventBrokerBranding branding, IUnifyEnginePlugInKey plugInKey)
   at Unify.Product.EventBroker.AgentEnginePlugInFactory.CreateComponent(IUnifyEnginePlugInFactoryInformation`1 factoryInformation)
   at Unify.Framework.DependencyPlugInGenerator`4..ctor(ICollection`1 plugInGenerator, IPlugInFactory`2 factoryInformationFactory)
   at Unify.Framework.UnifyEngine`1..ctor(TBranding branding, IEnumerable`1 additionalPlugInFactories, DirectoryInfo executingAssemblyLocation, IsolatedStorageFile isolatedStorageLocation)
   at Unify.Product.EventBroker.EventBrokerSer...</data>
  </eventdata>
</event>

Log Name:      Application
Source:        UNIFYNow
Date:          22/08/2019 3:45:13 PM
Event ID:      0
Task Category: None
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      D-OCCCP-IM303.dbb.local
Description:
Error - The following occurred in module: General server error: Could not load type 'Unify.Product.EventBroker.MIMReferenceRepository' from assembly 'Unify.EventBroker.Agents, Version=4.0.0.0, Culture=neutral, PublicKeyToken=84b9288cb2633de4'.

The following general server error occured:
System.TypeLoadException: Could not load type 'Unify.Product.EventBroker.MIMReferenceRepository' from assembly 'Unify.EventBroker.Agents, Version=4.0.0.0, Culture=neutral, PublicKeyToken=84b9288cb2633de4'.
   at Unify.Product.EventBroker.AgentEngine..ctor(IConfigurationEngine configurationEngine, ILicensingEngine licensingEngine, INotificationMessageService messageService, IIsolatedStoredValuesEngine storedValuesEngine, IScheduleComposite scheduler, IEventBrokerBranding branding, IUnifyEnginePlugInKey plugInKey)
   at Unify.Product.EventBroker.AgentEnginePlugInFactory.CreateComponent(IUnifyEnginePlugInFactoryInformation`1 factoryInformation)
   at Unify.Framework.DependencyPlugInGenerator`4..ctor(ICollection`1 plugInGenerator, IPlugInFactory`2 factoryInformationFactory)
   at Unify.Framework.UnifyEngine`1..ctor(TBranding branding, IEnumerable`1 additionalPlugInFactories, DirectoryInfo executingAssemblyLocation, IsolatedStorageFile isolatedStorageLocation)
   at Unify.Product.EventBroker.EventBrokerServiceEngine..ctor(DirectoryInfo executingAssemblyLocation, IsolatedStorageFile isolatedStorageLocation, IEventBrokerBranding branding)
   at Unify.Product.EventBroker.EventBrokerService.OnStart(String[] args)
Event Xml:
<event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <system>
    <provider name="UNIFYNow">
    <eventid qualifiers="0">0</eventid>
    <level>2</level>
    <task>0</task>
    <keywords>0x80000000000000</keywords>
    <timecreated systemtime="2019-08-22T05:45:13.639360700Z">
    <eventrecordid>535917</eventrecordid>
    <channel>Application</channel>
    <computer>D-OCCCP-IM303.dbb.local</computer>
    <security>
  </security></timecreated></provider></system>
  <eventdata>
    <data>Error - The following occurred in module: General server error: Could not load type 'Unify.Product.EventBroker.MIMReferenceRepository' from assembly 'Unify.EventBroker.Agents, Version=4.0.0.0, Culture=neutral, PublicKeyToken=84b9288cb2633de4'.

The following general server error occured:
System.TypeLoadException: Could not load type 'Unify.Product.EventBroker.MIMReferenceRepository' from assembly 'Unify.EventBroker.Agents, Version=4.0.0.0, Culture=neutral, PublicKeyToken=84b9288cb2633de4'.
   at Unify.Product.EventBroker.AgentEngine..ctor(IConfigurationEngine configurationEngine, ILicensingEngine licensingEngine, INotificationMessageService messageService, IIsolatedStoredValuesEngine storedValuesEngine, IScheduleComposite scheduler, IEventBrokerBranding branding, IUnifyEnginePlugInKey plugInKey)
   at Unify.Product.EventBroker.AgentEnginePlugInFactory.CreateComponent(IUnifyEnginePlugInFactoryInformation`1 factoryInformation)
   at Unify.Framework.DependencyPlugInGenerator`4..ctor(ICollection`1 plugInGenerator, IPlugInFactory`2 factoryInformationFactory)
   at Unify.Framework.UnifyEngine`1..ctor(TBranding branding, IEnumerable`1 additionalPlugInFactories, DirectoryInfo executingAssemblyLocation, IsolatedStorageFile isolatedStorageLocation)
   at Unify.Product.EventBroker.EventBrokerServiceEngine..ctor(DirectoryInfo executingAssemblyLocation, IsolatedStorageFile isolatedStorageLocation, IEventBrokerBranding branding)
   at Unify.Product.EventBroker.EventBrokerService.OnStart(String[] args)</data>
  </eventdata>
</event>