Cisco VPN disconnects after 5 seconds with error 422

I'm trying to connect to my university's server with VPN using Cisco VPN Client version 5.0.04, but after 5 seconds it disconnects with the error message 422: Lost contact with the secure gateway. Check your connection.

From my research on the net it seems this could be because it tries to find my IP, and finds out that this is 127.0.0.1. Then 5 seconds later it discovers that I have a new IP (my actual IP), and it disconnects because I'm not allowed to change IP.

Does anyone know how I could fix this, or if there is another reason i get this error?

Update

I looked through the log, and found this error, which confirms what I thought, except it gets the correct IP first, then changes it to localhost.

87 18:56:53.250 08/24/09 Sev=Warning/3 CM/0xA3100027 Adapter address changed from 149.171.237.25. Current address(es): 127.0.0.1.

Based on this thread and this thread, it looks like there could be a number of reasons why the Cisco VPN client is returning this error. These reasons could include a routing conflict, conflict with a program on your computer (like Toshiba's ConfigFree utility), or some issues with NAT traversal. Good diagnostics would be trying to connect with a disabled firewall (as Col mentioned), trying to connect with a direct connection to the internet (not behind a router), and looking at the log (located in the Log tab of the VPN Client window). If you can't determine what the problem is, post the log in your question so someone else can look at it.

If you're connecting through a USB Key to access internet such as through movistar or Huawei connection or whatever you have, make sure that your Airport is turned off and you're not sharing internet.

If it's on, it registers two different IPs and won't work.