you open your project using Step5 (V6.x or V7.x) and then open any of the blocks. I usually try OB1 which is the base of nearly every project, so i miss all the fun of searching blocks.
After opening this block you'll see a F-key "x-ref", press it, a new menue of function keys opens including "create x-ref" or "generate" or something similar. (Sorry i just have to depend on memory, there's no system available to me currently). Now press f-key "vreate x-ref", wait a minute for the system to be done, and you got the x-ref the converter is needing to get its job done.
You just need to leave the block unchanged (best advice use ESC), leave the S5 project and close Step5.