Here's how you can open a later version of an RSLogix 5000 program with an earlier version of the software:
Be sure to save a copy of the original!!!
1. Have somebody who has v13 of the software save the file using the .L5K extension.
2. Open the .L5K file using Word Pad. You should see something similar to the following file: (which has been cropped for uploading)
3. The key things to change are the IE Ver and, if necessary, the major revision numbers of any controllers in the program.
4. Change the IE Ver number from "2.3" (which is for version 13 of the software) to "2.2" (for version 12).
Note: You can check the correct version number by exporting an L5K file from a version 11 or 12 project, and matching this number.
5. You will also need to change the major revision number of the controller to the version you are using.
6. When you have finished the changes, you can use the Open/Import feature to import the L5K file back into RSLogix 5000.
Hope this gets you started!
Rick