Resolving The Problem

QUESTION:

How to override the default editor associated to a given extension in Microsoft Visual Studio .Net?

ANSWER:

It may happen that Rational XDE is set in Microsoft Visual Studio .Net. as the default editor associated to a specific file extension , that another installed application uses.
Visual Studio .Net stores a list of applications that are associated with specific file extensions.
These settings are separate from those at the operating system level.
Even if double clicking in the Windows Explorer on a file with extension '.xxx' fires application 'X', it may be that XDE is invoked to open such file within Visual Studio .Net.

Under these circumstances, one may get the following error when trying to open a file that should be associated to an application different to XDE:
*********************************************
Modeler Error: Failed to load Model file: 'File_Path.xxx'
Details: Unable to open model file: 'File_Path.xxx'
Parser Error (line2): Bad namespace received with token '<null>' during input.
*********************************************
(XDE is trying to treat the file as a model file and does not recognize the syntax and therefore throws the above error).

To correct such behavior, one can proceed as follows:
1. Start Visual Studio .Net
2. Choose File->New
3. Select the wanted kind of file
4. Expand the drop down list in the Open button and choose: Open with
5. Select the correct application that should handle this kind of file
6. Click on the button: Set as default
7. Choose: Open

This changed preference will be stored in the registry for the current user.
One can inspect with 'regedit' the following registry hive, to see the changes:

[HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\7.0\Default Editors\<extension>]

where <extension> indicates the extension (without the initial dot), such as 'xxx' in the above example.