Attempting to call the IApplication::OpenDocument method from within a modal dialog box generates a permissions error.
When programming in VB6, the error message "Permission Denied" may occur with an error number of 70.
When programming in Visual Studio .NET, an exception of type System.UnauthorizedAccessError may occur and return "Access Denied".
OpenDocument and NewDocument cannot be called when there is a modal dialog box present in the application. This is prevented by the internal design of ArcGIS.