1) Open the OAR file with WINZIP (depending on your version of Windows you might be able to right-click on the file in Windows Explorer and do an “Open with…” or you might need to temporarily change the file extension to .ZIP.
2) Double-click on the file “metadata.foc” (it will open in whatever your default text editor is; if it doesn’t and instead asks you to choose an application to open it with, use Notepad or something similar).
3) Find this tag near the beginning of the file: <session serverVersion="[some_number_here]">
4) Change that number to the base value for whatever version you want to be able to associate it with; “8.0” for SQL Server 2000, “9.0” for SQL Server 2005, etc.
5) Save and close the text editor.
6) Winzip will ask you if you want to “Update archive with this file?”. Click ‘Yes”.
7) If you had to change the file extension from OAR to ZIP previously, change it back to OAR.
Now you will be able to attach this OAR file to any data source of at least the version you set in the metadata.foc file.