I tried an installation on DNN 3.1.1 and got the following issue during PA installation, when registering Desktop-Modules:
FehlerSystem.Data.SqlClient.SqlException: Verletzung der UNIQUE KEY-Einschränkung 'IX_DNN_ModuleDefinitions'. Ein doppelter Schlüssel kann in das DNN_ModuleDefinitions-Objekt nicht eingefügt werden. Die Anweisung wurde beendet. at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream) at System.Data.SqlClient.SqlCommand.ExecuteScalar() at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteScalar(SqlConnection connection, CommandType commandType, String commandText, SqlParameter[] commandParameters) at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteScalar(String connectionString, CommandType commandType, String commandText, SqlParameter[] commandParameters) at Microsoft.ApplicationBlocks.Data.SqlHelper.ExecuteScalar(String connectionString, String spName, Object[] parameterValues) at DotNetNuke.Data.SqlDataProvider.AddModuleDefinition(Int32 DesktopModuleId, String FriendlyName, Int32 DefaultCacheTime) at DotNetNuke.Modules.Admin.ResourceInstaller.PaDnnInstallerBase.RegisterModules(PaFolder Folder, ArrayList Modules, ArrayList Controls) at DotNetNuke.Modules.Admin.ResourceInstaller.PaDnnInstallerBase.Install(PaFolderCollection folders) at DotNetNuke.Modules.Admin.ResourceInstaller.PaInstaller.Install()
Translation: Database is complaining about vulnaration against unique key contraint 'IX_DNN_ModuleDefinitions': A duplicate key cannot be added to object DNN_ModuleDefinitions.