If you use Windows ® Explorer to open a SolidWorks file, and you have multiple versions of SolidWorks installed on your computer, a dialog box prompts you to select which version to use to open the file.
The Multiple Versions dialog box displays up to the three most recent versions of SolidWorks that are installed on your computer. For example, if SolidWorks versions 2009 to 2013 are installed, you can choose to open the file with version 2011, 2012 or 2013.
If you want to use the selected version to open all of your SolidWorks files, you can suppress the dialog box by selecting Do not show this again.
You can reset files with the version of SolidWorks that last saved them from and clicking Restore file Associations. For example, you might use this if you had SolidWorks 2012 SPO4 and the SolidWorks 2013 beta on your machine, and then uninstalled the SolidWorks 2013 beta.
To restore file associations, you must launch SolidWorks with Run as administrator privileges. These steps may vary per operating system. For information on how to Run as administrator, consult the Microsoft Knowledge Base.