You are attempting to open a file created in version 3 of Numbers (or a more recent version).
The version of Numbers attempting to open the document is Numbers 2.x, otherwise known as Numbers '09.
Version 3 was a 'from the ground up' rewrite. Among the changes was a change in the structure of the file format used to store .numbers documents.
Numbers '09 files were a package that included (and required) an index.xml file.
Numbers v3 (and later) versions do not require (or contain) an index.xml file.
In Finder, right click on the file to open the open-with menu and choose the Numbers with the highest version number (remembering that Numbers '09 is version 2.x and Numbers '08, which is unlikely to be on the list, is version 1.x).
To tell your Mac to use the version chosen here to always use that version, click once on the filename, then press command-I to Get Info.
In the info pane, go to the Open with section and choose the same version of Numbers as you did above. Then check Change All to make that version of Numbers the default version to open all files with the .numbers extension.
Regards,
Barry
Regards,
Barry