We have an occasional problem with a cisco vpn concentrator (sorry dont have model details currently)
If we lose power to the device, most recently through a ups failure when it comes back up clients accessing the site via cisco vpn client software, currently v4.01 can have problems with their username becoming case sensitive.
If the username has been entered in active directory in uppercase the user must use uppercase in the client at which point they gain access.
The problem has been resolved a couple times by our cisco support but this is the third time it has re-occurred and we're wondering if it is a known issue as we don't get a satisfactory response from our support.