In 07.02.00_Application.log.resources hidden away in the depths of the site folder structure I found this.
Any comments or preferably a solution DNN Corp?

Error: Cannot insert duplicate key row in object 'dbo.ModuleDefinitions' with unique index 'IX_ModuleDefinitions'. The duplicate key value is (Module Creator).
The statement has been terminated. at System.Data.SqlClient.SqlConnection. (SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
at System.Data.SqlClient.SqlDataReader.TryConsumeMetaData()
at System.Data.SqlClient.SqlDataReader.get_MetaData()
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
at System.Data.SqlClient.SqlCommand.ExecuteScalar()
at PetaPoco.Database.ExecuteScalar[T](String sql, Object[] args)
at DotNetNuke.Data.PetaPoco.PetaPocoHelper.ExecuteScalar[T](String connectionString, CommandType type, String sql, Object[] args)
at DotNetNuke.Data.DataProvider.AddModuleDefinition(Int32 desktopModuleId, String friendlyName, String definitionName, Int32 defaultCacheTime, Int32 createdByUserID)
at DotNetNuke.Entities.Modules.Definitions.ModuleDefinitionController.SaveModuleDefinition(ModuleDefinitionInfo moduleDefinition, Boolean saveChildren, Boolean clearCache)
at DotNetNuke.Services.Upgrade.Upgrade.AddModuleDefinition(String desktopModuleName, String description, String moduleDefinitionName, String businessControllerClass, Boolean isPortable, Boolean premium, Boolean admin)
at DotNetNuke.Services.Upgrade.Upgrade.UpgradeToVersion720()
at DotNetNuke.Services.Upgrade.Upgrade.UpgradeApplication(String providerPath, Version version, Boolean writeFeedback)

Hi Richard. Ah ha. I had the stand alone module creator 1.0.0 installed. This has now been incorporated into DNN 7.2.0 so now I have two Module Creators listed in the extensions, a 1.0.0 and a 1.1.0 which I assume is the old standalone one (1.0.0) and the incorporated one (1.1.0). Looks like an uninstall of Module Creator is required before upgrading. I'll try it and post back.