Thats funny, I posted a reply and it didn't show up.
Looking at your thoughts Peter I turned off domain control, and turned it back on and the VPN started working fine, at least for one day. Went back to it the next day and prior symptoms were back.
Answering your questions - we had a fully patched 6.03b - and ARE running 6.0 final. Plenty of disk space, less than 10% used.
Am testing 6.01 on my box now prior to moving it to the office production machine. Need to be cautions here, better safe than sorry.
Cheers!