The index.xml file is missing I like using numbers 2.2 but also have 4.3.1 installed. I would 
much rather use 2.2. as its been working all along and because I like the format bar which is not in 4.3.1.

I've been using "Open With" to get my files to open in 2.2, but now when I try to open in 2.2 I get a "The index.xml file is missing" error message and can only open them in 4.3. 

How can I get back to 2.2?
Just "spitballing" here, but do you have a Time Machine backup?  

If so, search it for 'index.xml'.  If you find a file that resides in a Numbers 2.2-related folder, copy it to the present and put it in the same spot where you found it in the "past".