Fixing error The block or page '[ContentTypeName]' has not been synchronized yet

Sometimes the database schema synchronization for some reason does not work and you end up with an error message like this:

Initialize action failed for 'Initialize on class EPiServer.Initialization.Internal.ModelSyncInitialization, EPiServer, Version=11.11.0.0, Culture=neutral, PublicKeyToken=8fe83dea738b45b7'
System.InvalidOperationException: The block '[Namespace].[ContentTypeName]' has not been synchronized yet
   at EPiServer.DataAbstraction.RuntimeModel.Internal.PropertyDefinitionSynchronizer.LoadBlockDefinitionType(PropertyDefinitionModel map)
   at EPiServer.DataAbstraction.RuntimeModel.Internal.PropertyDefinitionSynchronizer.ResolveType(PropertyDefinitionModel model)
   at EPiServer.DataAbstraction.RuntimeModel.Internal.PropertyDefinitionSynchronizer.CreatePropertyDefinition(PropertyDefinitionModel model, Int32 contentTypeID)
   at EPiServer.DataAbstraction.RuntimeModel.Internal.ContentTypeModelRegister.CommitProperties(Boolean deleteUnusedTypes)
   at EPiServer.DataAbstraction.RuntimeModel.Internal.ContentTypeModelScanner.Sync(Boolean commitChanges)
   at EPiServer.Initialization.Internal.ModelSyncInitialization.Initialize(InitializationEngine context)
   at EPiServer.Framework.Initialization.Internal.ModuleNode.<>c__DisplayClass2_0.<Initialize>b__0()
   at EPiServer.Framework.Initialization.Internal.ModuleNode.Execute(Action a, String key)
   at EPiServer.Framework.Initialization.Internal.ModuleNode.Initialize(InitializationEngine context)
   at EPiServer.Framework.Initialization.InitializationEngine.InitializeModules()

Even if you do an update the error will still be there and the only way to solve it (that I have seen) is to reset the affected content type by setting the property ModelType to null.

You should only do this for you own content types and not system types and you should always tripple check so you do not miss out on the Where clause.

You can do it with a script like this:

Update tblContentType
Set ModelType = null
Where [Name] = '[ContentTypeName]'

Disclaimer: You should not be updating information inside the Episerver Database if you do not know what you are doing. I give you this tip because it worked for me and if you do it, be sure to take a backup of the database first and run it with care!