maybe this video can help you

https://www.youtube.com/watch?v=uZsB4vNOKtY&feature=emb_logo

From the log it seems that you selected Channel 4 for both input and output. Select different channels for them. Check which ports you connected your SDI cables to on your AJA cards, and use the channel number accordingly.

Also please note that normally you should not use the Video Device Out node for outputting to SDI.  It's better to setup the SDI out in the Startup Configuration, please check the video Ahmed recommended above.