Felt a bit silly even just asking this here.
I'm getting exactly the same problem with one of my SA4000's and ACE, but haven't had a problem before. What version of the IVE O/S are you on? I'm on 6.3R3.
There is a port blocked between IVE internal IP and RSA Server IP.
I think it was UDP5500 or something like that. Read the Documentation.
Pinging RSA Server is not enough. Check Firewall between the two devices.
Have you defined the sslvpn box as an an "agent host" on the RSA server?