Running an old version and a new version of CI on same server - can I?

[eluser]PhilTem[/eluser]
Sure you can run two different installs on the same server as long as they are physically separated (i.e. they are in different folders) and you link them correctly in your index.php file it should work. At least from a theoretical point of view. What you need to consider though: Changing the system from 1.6.1 to 2.1.2 might if not will brake some dependencies and you will have some errors to solve just because it is a major upgrade rather than a minor one

But if you don't mind running into these kind of problems you can have two different versions of CI running on your server with ease.