I think the OPs problem is that the new exchange plugins for r12 to cs4 dont seem to work – rather than him not knowing how to use them. Ive had the same problem.
I seem to have just gotten round this by opening the aec file in text edit and removing the only line i could see that didnt appear in aecs exported from 11.5.
the line i removed is
“VERSION 2” -without quotes – and appears just after the word “LOCAL”