Trying to burn blu-ray via ISO image- No longer working

Please help if you can! This used to work for me but no longer does since upgrading my OS system to El Capitan. I've tried on my late 2011 iMac as well as my 2014 macbook pro- both with no success. I get the same series of messages: Error code 3, try burning at slower speed(s), or incompatible media, etc... Usually a different message pops up each time.

The external drive is a SamsungSE-506. Both systems won't even recognize the device unless I open disk utility. I am able to start the burn through finder (as I have now learned it is approached now here) but it won't finish the job. Is this just my samsung device? Is it the discs (phillips)? Like I said, both worked in previous projects but now that I have upgraded to El capitan I am running into this problem. Maybe my samsung drive can't keep up with the newer OS?

PLEASE HELP. I'll buy a new drive if I need to but I'd rather not being that this one still functions.