system preferences hangs when attempting VPN

Hello folks,

I have a set of VPNs I regularly use, and these were all happily configured and running on my iMac running OSX 10.6.8 until sometime recently where something went wrong. Now, whenever I select a VPN on the Network page and click Connect, the "Connecting..." words appear under the VPN in question, and the system preference window freezes up. After a few minutes, I get an error message stating that the remote device has stopped responding. The system preferences window never recovers - on mousover I get the progress disk thing, and the "Connecting..." never goes away.

I do know the VPN servers are functioning - I use the same servers with my iPad with no issues. Any thoughts?