EXR with merge not working for me

I have multiple EXR files that I can't composite a simple A over B, I'm able to with TIFF Checkerboard but not with Redshift AOV EXR's with a black background? I'm sure I'm missing something here as I'm a Fusion Noobie!

can you post a screenshot or something which shows your problem?

your description is very vague tp see any problem