datagroup value set to SSL?

Interesting. So if you do no (client side or server side) SSL, just port 80 on the VIP load balancing to port 80 pool members, I'm assuming that doesn't work, correct? From the described error message it sounds like the application is expecting and requires that you talk to it over SSL. A 500 error means you're actually getting to the web server, so at the very least you need a server SSL profile and nodes on port 443 (or whatever SSL port they listen on). I'd start with the 'insecure_compatible' server SSL profile as it has the lowest set of requirements, and I'd also remove the HTTP profile until you have good data flow.