If you have ExtendSim 10 as well as a prior release, such as ExtendSim 9, installed on the same computer, double-clicking a model file might not open the release that you want because:

• The ExtendSim release that was installed last will automatically be the one that gets opened when you double-click a model file, even if the model was created in a different release.
• Even if ExtendSim 10 was installed last, double-clicking a model file could still launch a prior release, especially if you've been using ExtendSim for many years.

Solutions:

1. If you have Windows 10 and want to change all model (.mox) files to open with a specific ExtendSim release:
   • Right-click a model file, go to Properties and open the General tab. Next to Opens with:, click the Change button.
   • Scroll through the list and select which ExtendSim application you want to open when you double-click a model file. If the desired application isn't at the top of the list, click "More Apps"and scroll through the longer list.
   • The properties of all model files will be changed, so you only have to do this with one model file.
2. If you have Windows 10 and want to change a single model (.mox) file to open with a specific ExtendSim release:
   • Right-click a model file, choose Open with:
   • Scroll through the list and select which ExtendSim application you want to open when you double-click a model file. If the desired application isn't at the top of the list, click Choose another app and scroll through the longer list.
   • The properties of the selected model file will be changed.
     
     Note: If the ExtendSim release you want doesn't appear in the list, the Windows registry is confused. Please see #4 on this list.
3. Launch whichever ExtendSim release you want to open when you double-click a model file.
• Since the application will be making a change to the registry, this requires that ExtendSim be Run as Administrator.
• In the File menu, choose the command Update Launch Control. By clicking OK, you will set the system's registry to always launch that application when a model or library file is double-clicked.
  
  Note: If this doesn't work, see #4, below.
4. Change the Default app using Windows Settings.
• Go to Settings > Apps > Apps & Features.
• Select Default apps in the list on the left side of the window.
• At the bottom of the list, select to Choose default apps by file type or Select a default app by file type.
• In the left column, locate the .mox file type. Click on the icon to its right, then and select the appropriate ExtendSim release from the list.
  
  Note: If the ExtendSim release you want doesn't appear in the list, the Windows registry is confused. Please see #4 on this list.
5. If none of the above solutions work, you have probably installed many different releases of ExtendSim over the years. Even after the applications have been uninstalled, there can be files, folders, and registry entries left on the system, causing program data to be left behind. Windows advisor recommended that you using Revo Uninstaller, a free application that is not a registry cleaner. Revo Uninstaller uninstalls the selected app, then allows you to scan for leftover files, data, and registry entries that you can delete. After using it, you'll need to reinstall whichever ExtendSim applications you want to use. Then use on of the options above to set which application launches when you double-click a model file. Read Revo Uninstaller instructions and be sure to back up your computer and save any custom models, libraries, and other files before using it. After using it, restart your computer.