Installing demo templates on a CMS6 site fails with error message: "You cannot call a method on a null-valued expression."

OS is Windows 7, Installing a new CMS 6 site with public templates worked fine. Seem to be related to the xml update part of the installation:

"Copied Web.Config.xmlupdate

Copied Web.Config.xmlupdate
An unhandled error has occured: When executing
At C:\Program Files\EPiServer\CMS\6.0.530.0\Install\Modules\DemoTemplates\Install Demo Templates.ps1:202 char:48+ $startPageID = $node.siteSettings.GetAttribute <<<< ("pageStartId")
True=Get-EPiIsBulkInstallingAn error has occured and the transaction will be rolled backThe was an error during the rollback phase. Your system may be left in an unstable conditionObject reference not set to an instance of an object.System.NullReferenceException: Object reference not set to an instance of an object.   at System.Configuration.Install.Installer.Rollback(IDictionary savedState)   at EPiServer.Install.InstallationManager.RollbackBulkInstall()Object reference not set to an instance of an object.The was an error during the rollback phase. Your system may be left in an unstable conditionObject reference not set to an instance of an object.System.NullReferenceException: Object reference not set to an instance of an object.   at System.Configuration.Install.Installer.Rollback(IDictionary savedState)   at EPiServer.Install.InstallationManager.RollbackBulkInstall()Object reference not set to an instance of an object.Failed to rollback creation of directory C:\EPiServer\Sites\CMS 6 demositeThe process cannot access the file 'C:\EPiServer\Sites\CMS 6 demosite' because it is being used by another process.Rolledback
An unhandled error has occured:You cannot call a method on a null-valued expression.When executing
At C:\Program Files\EPiServer\CMS\6.0.530.0\Install\Modules\DemoTemplates\Install Demo Templates.ps1:202 char:48+ $startPageID = $node.siteSettings.GetAttribute <<<< ("pageStartId")
=Get-EPiIsBulkInstallingError - System.Management.Automation.RuntimeException: You cannot call a method on a null-valued expression.   at System.Management.Automation.ParserOps.CallMethod(Token token, Object target, String methodName, Object[] paramArray, Boolean callStatic, Object valueToSet)   at System.Management.Automation.MethodCallNode.InvokeMethod(Object target, Object[] arguments, Object value)   at System.Management.Automation.MethodCallNode.Execute(Array input, Pipe outputPipe, ExecutionContext context)   at System.Management.Automation.AssignmentStatementNode.Execute(Array input, Pipe outputPipe, ExecutionContext context)   at System.Management.Automation.StatementListNode.ExecuteStatement(ParseTreeNode statement, Array input, Pipe outputPipe, ArrayList& resultList, ExecutionContext context)"