Kind of tricky..
I have actually NOT found one set resolution to this issue, but I have seen it quite a few times, it seems to happen more with remote users than in other situations.
One: Make sure the group authorization name is correct.
Two: Deleting the password, not changing it, but deleting it, then re-apply the password back.
Three: If the client is behind a firewall, the firewall may have to be disabled. ( not the VPN stateful firewall option ).
Four: Look at changing the transport modes. By default it will use UDP, Try using TCP/IPSEC instead, it should force the connection.
Hopefully some of these will work for you.
Let me know...
