I just checked my ASA 5520 config and the netflow-related items match yours so I believe you are good to go on the ASA side of things - I had the NetFlow tool Scrutinizer running on this same server (I am now running RNA on this server) before, and it showed NetFlow data for my ASAs. I too am not having luck in getting the RNA to work with my ASAs however - I also see nothing in the Flow Type column for the ASA's interfaces yet I see traffic data for them, in RNA. I also get that error when I select an interface with traffic data, and click Start Flow Capture. I too have confirmed that the udp 2055 traffic is hitting the server and that per my netstat -an output the server is listening on udp 2055. And I double-checked and see that no other netflow applications are running on this server. I'll certainly advise if I find anything out. Thanks!
ASAs and Solarwinds don't play well together sometimes. There was an issue where Solarwinds did not support the NSEL flexible template format that ASAs used. This was apparently fixed in NTA, but I don't know about RTNA. The ASA netflow format is a bit wacky in fact - there are several collectors that have problems reading the data. You are in a bit of a catch 22 here, just sit and hope someone has got it to work here on Thwack, or buy NTA, which you would get support for, but not need because NTA seems to collect ASA flows properly.