The unit works fine with the two main CTs connected. When I connect the expansion cable to the expansion unit, the LED stops blinking and it stops working. When I remove it, it starts blinking again.
I just recently experienced this while installing my two new Vue units. I tried many different troubleshooting options including switching expansion modules and main units. Ultimately I contacted customer support and they have sent me a replacement unit. I found email to be the best way to contact customer support, good luck.