Sorry for adding my 2c worth here WLB!
So it sounds like the forwarding VS is working as you can ping through the BIG-IP to and from the servers. Is it the application VIPs that are not working then?
If so, a shot in the dark here. Could it be the auto-lasthop feature getting in the way? See http://support.f5.com/kb/en-us/solutions/public/9000/400/sol9487.html
If not what happens if you disable your application VIP and access the application server directly (over whatever protocol you're using e.g. HTTP)? This way the forwarding VIP would match the traffic and deliver the traffic to the backend server direct.
Just thoughts.
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